Per-binding throughput benchmarks + test-coverage gaps (#246)

Adds a `throughput` benchmark to every target and closes two small
test-coverage documentation/QA gaps. One PR, no merge of binding code beyond
the additive benchmarks and one C test.

## 1. Per-binding throughput benchmarks (all 9 targets)

Each benchmark feeds a deterministic synthetic OHLCV series through three
indicators chosen by **FFI call-signature archetype** (not algorithm — the same
Rust core runs underneath all bindings):

- `SMA(20)` — 1-in → 1-out (baseline boundary cost)
- `ATR(14)` — multi-in → 1-out (input marshalling)
- `MACD(12,26,9)` — 1-in → multi-out (output marshalling)

Streaming is timed for all three; batch for the single-output SMA and ATR
(median of 3 runs, after a warmup pass).

New: Python (PyO3), WASM, C (CMake), C# (Stopwatch), Go, Java (FFM), R, and the
Rust core baseline (`examples/rust/.../throughput.rs`, **no FFI** — the ceiling
the bindings are measured against and the value their batch paths converge
towards). Node already had `throughput.js`.

**Not a speed claim:** there is no comparable streaming TA library for C, C#,
Go, Java, R or WASM to compare against, so these are raw per-binding throughput
numbers documenting each language's FFI overhead — see BENCHMARKS.md §3. The
"Wickra is fast" claim still lives in §1/§2 (Rust core + the Python/Rust
cross-library runs).

## 2. README `## Testing`: C# and C bullets

The section listed every layer except C# and C, even though both have suites.
Adds the two missing bullets.

## 3. C archetype ctest

`examples/c/archetypes.c` drives one indicator per FFI archetype through the
real C boundary (scalar + batch==streaming, multi-output, bars, profile, array
input) plus reset, invalid-parameter and NULL-safety — the C counterpart of the
Go/R/Java archetype suites. Runs on three OSes via the existing CMake/ctest.

## Notes

- Benchmarks are not CI-gated (manual-run scripts, like the existing
  `throughput.js`); no `ci.yml`/`release.yml` changes.
- Docs: BENCHMARKS.md §3, a `## Benchmark` section in every binding README, a
  CHANGELOG entry.
- Verified locally by running: Rust, Python, C, C#, Go, Java (real numbers); the
  C archetype ctest with `-Wall -Wextra -Wpedantic -Werror`. WASM and R are
  API-correct and syntax-checked but need their own toolchains to run.

bindings/java/README.md

@@ -76,6 +76,19 @@ values — the equivalence is enforced by the test suite. Multi-output indicator
 indicator owns a native handle freed by a `Cleaner`; `close()` releases it
 eagerly (use try-with-resources).
 
+## Benchmark
+
+`benchmarks/` reports streaming and batch updates-per-second for `SMA`, `ATR`
+and `MACD`. It measures this binding's FFI overhead, not a cross-library ratio
+(the same Rust core runs under every binding) — see the repository
+[BENCHMARKS.md](https://github.com/wickra-lib/wickra/blob/main/BENCHMARKS.md) §3.
+
+```bash
+cargo build -p wickra-c --release
+mvn -q install -DskipTests
+mvn -q -f benchmarks exec:exec -Dexec.mainClass=org.wickra.benchmarks.Throughput
+```
+
 ## Documentation
 
 The full indicator catalogue, guides, quickstarts, and API reference live in

bindings/java/benchmarks/pom.xml

@@ -0,0 +1,57 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.wickra.benchmarks</groupId>
+  <artifactId>wickra-benchmarks</artifactId>
+  <version>0.8.2</version>
+  <packaging>jar</packaging>
+
+  <name>Wickra Java benchmarks</name>
+  <description>Throughput benchmark for the Wickra Java binding.</description>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.release>22</maven.compiler.release>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.wickra</groupId>
+      <artifactId>wickra</artifactId>
+      <version>0.8.2</version>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.13.0</version>
+      </plugin>
+
+      <!--
+        Run the benchmark in a forked JVM with native access granted:
+          mvn exec:exec -Dexec.mainClass=org.wickra.benchmarks.Throughput
+        Requires the C ABI library and the installed binding; see Throughput.java.
+      -->
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>exec-maven-plugin</artifactId>
+        <version>3.2.0</version>
+        <configuration>
+          <executable>${java.home}/bin/java</executable>
+          <arguments>
+            <argument>--enable-native-access=ALL-UNNAMED</argument>
+            <argument>-classpath</argument>
+            <classpath/>
+            <argument>${exec.mainClass}</argument>
+          </arguments>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

bindings/java/benchmarks/src/main/java/org/wickra/benchmarks/Throughput.java

@@ -0,0 +1,149 @@
+package org.wickra.benchmarks;
+
+import java.util.Arrays;
+import java.util.Locale;
+import org.wickra.Atr;
+import org.wickra.MacdIndicator;
+import org.wickra.Sma;
+
+/**
+ * Throughput benchmark for the Wickra Java binding.
+ *
+ * <p>Measures how many indicator updates per second the binding sustains, both
+ * per-tick (streaming {@code update}) and bulk ({@code batch}), over a synthetic
+ * OHLCV series. It is the Java counterpart of the Node {@code throughput.js} and
+ * the Rust criterion benches: it benchmarks Wickra's own O(1) streaming engine
+ * across the Java FFM &lt;-&gt; C-ABI boundary (there is no comparable streaming
+ * TA library on Maven Central to compare against), so the headline number is raw
+ * per-binding throughput / FFI overhead, not a cross-library ratio.
+ *
+ * <p>Three indicators are timed, chosen by FFI call-signature archetype rather
+ * than algorithm: SMA (1-in -&gt; 1-out), ATR (multi-in -&gt; 1-out), and MACD
+ * (1-in -&gt; multi-out). Streaming is timed for all three; batch only for the
+ * single-output SMA and ATR (multi-output batch is not exposed uniformly).
+ *
+ * <p>Install the binding and build the C ABI library first, then run from the
+ * repo root:
+ *
+ * <pre>
+ *   cargo build -p wickra-c --release
+ *   mvn -q -f bindings/java install -DskipTests
+ *   mvn -q -f bindings/java/benchmarks exec:exec -Dexec.mainClass=org.wickra.benchmarks.Throughput
+ * </pre>
+ */
+public final class Throughput {
+    private Throughput() {}
+
+    public static void main(String[] args) {
+        int bars = 200_000;
+        for (int i = 0; i < args.length - 1; i++) {
+            if (args[i].equals("--bars")) {
+                try {
+                    int n = Integer.parseInt(args[i + 1]);
+                    if (n >= 1000) {
+                        bars = n;
+                    }
+                } catch (NumberFormatException ignored) {
+                    // keep default
+                }
+            }
+        }
+
+        // Deterministic synthetic OHLCV (no RNG, so runs are comparable).
+        double[] open = new double[bars];
+        double[] high = new double[bars];
+        double[] low = new double[bars];
+        double[] close = new double[bars];
+        double[] volume = new double[bars];
+        double[] timestamp = new double[bars];
+        for (int i = 0; i < bars; i++) {
+            double mid = 100 + Math.sin(i * 0.001) * 20 + i * 1e-4;
+            double c = mid + Math.sin(i * 0.05) * 2;
+            close[i] = c;
+            open[i] = mid;
+            high[i] = Math.max(c, mid) + 1.5;
+            low[i] = Math.min(c, mid) - 1.5;
+            volume[i] = 1000 + (i % 97) * 13;
+            timestamp[i] = i;
+        }
+
+        final int n = bars;
+
+        // SMA (scalar 1-in/1-out), ATR (multi-in/1-out), MACD (1-in/multi-out).
+        Indicator[] indicators = {
+            new Indicator("SMA(20)",
+                () -> {
+                    try (Sma ind = new Sma(20)) {
+                        for (int i = 0; i < n; i++) {
+                            ind.update(close[i]);
+                        }
+                    }
+                },
+                () -> {
+                    try (Sma ind = new Sma(20)) {
+                        ind.batch(close);
+                    }
+                }),
+            new Indicator("ATR(14)",
+                () -> {
+                    try (Atr ind = new Atr(14)) {
+                        for (int i = 0; i < n; i++) {
+                            ind.update(open[i], high[i], low[i], close[i], volume[i], (long) timestamp[i]);
+                        }
+                    }
+                },
+                () -> {
+                    try (Atr ind = new Atr(14)) {
+                        ind.batch(open, high, low, close, volume, timestamp);
+                    }
+                }),
+            new Indicator("MACD(12,26,9)",
+                () -> {
+                    try (MacdIndicator ind = new MacdIndicator(12, 26, 9)) {
+                        for (int i = 0; i < n; i++) {
+                            ind.update(close[i]);
+                        }
+                    }
+                },
+                null), // multi-output: streaming only
+        };
+
+        System.out.printf(Locale.ROOT, "Wickra Java throughput - %,d bars (median of 3 runs)%n%n", bars);
+        System.out.printf(Locale.ROOT, "%-22s%20s%18s%n", "Indicator", "streaming (Mupd/s)", "batch (Mupd/s)");
+        System.out.println("------------------------------------------------------------");
+
+        for (Indicator ind : indicators) {
+            String streamMups = String.format(Locale.ROOT, "%.1f", mups(bars, timeNs(ind.stream)));
+            String batchMups = ind.batch == null
+                ? "-"
+                : String.format(Locale.ROOT, "%.1f", mups(bars, timeNs(ind.batch)));
+            System.out.printf(Locale.ROOT, "%-22s%20s%18s%n", ind.name, streamMups, batchMups);
+        }
+
+        System.out.println(
+            "\nMupd/s = million indicator updates per second. Streaming is the per-tick\n"
+            + "update path crossing the Java FFM<->C-ABI boundary once per value; batch is\n"
+            + "the bulk array path (one boundary crossing). Higher is better. Numbers are\n"
+            + "machine-dependent - use them for relative comparison, not as a speed claim.");
+    }
+
+    private static double mups(int bars, double ns) {
+        return bars / (ns / 1e9) / 1e6;
+    }
+
+    // Median elapsed-ns over a few repetitions, after one warmup pass.
+    private static double timeNs(Runnable fn) {
+        fn.run(); // warmup (JIT + cache)
+        final int reps = 3;
+        double[] samples = new double[reps];
+        for (int r = 0; r < reps; r++) {
+            long t0 = System.nanoTime();
+            fn.run();
+            samples[r] = System.nanoTime() - t0;
+        }
+        Arrays.sort(samples);
+        return samples[reps / 2];
+    }
+
+    private record Indicator(String name, Runnable stream, Runnable batch) {}
+}