feat(data): expose CandleReader (CSV) natively in all 10 languages (#311)

Add the data-layer CSV candle reader to every binding so loading OHLCV
candles from a CSV no longer needs a per-language CSV/dataframe dependency.

- C ABI: wickra_candle_reader_new(bytes, len) / _count / _read / _free over
  an opaque CandleReader handle (parse the whole buffer up front, then drain).
- Native: Node/WASM CandleReader.read() -> Candle[], Python read() -> list[tuple].
- C-ABI languages: Go Read() []Candle, C# Candle[] Read(), Java Candle[] read(),
  R read() S3 generic (n x 6 matrix); C / C++ call the C ABI directly.
- Cross-language golden testdata/golden/data_csv*.csv pins the parsed candles
  bit-for-bit across every binding.

Verified locally across Rust (test+clippy+fmt), Node, WASM, Python, C#, Go,
Java, R, and the C/C++ cmake parity suite.

bindings/wasm/src/lib.rs

@@ -16101,3 +16101,34 @@ impl WasmResampler {
         }
     }
 }
+
+// ===== Data layer: CSV candle reader =====
+
+/// Parse OHLCV candles from a CSV string (header `timestamp,open,high,low,close,
+/// volume`; a leading UTF-8 BOM is stripped).
+#[wasm_bindgen(js_name = CandleReader)]
+pub struct WasmCandleReader {
+    candles: Vec<wc::Candle>,
+}
+
+#[wasm_bindgen(js_class = CandleReader)]
+impl WasmCandleReader {
+    /// Parse the whole CSV up front; throws on a malformed header or row.
+    #[wasm_bindgen(constructor)]
+    pub fn new(csv: &str) -> Result<WasmCandleReader, JsError> {
+        let mut reader =
+            wickra_data::csv::CandleReader::from_reader(csv.as_bytes()).map_err(map_data_err)?;
+        let candles = reader.read_all().map_err(map_data_err)?;
+        Ok(Self { candles })
+    }
+
+    /// Return every parsed candle as a `{ open, high, low, close, volume,
+    /// timestamp }` object.
+    pub fn read(&self) -> Array {
+        let arr = Array::new();
+        for &c in &self.candles {
+            arr.push(&candle_object(c));
+        }
+        arr
+    }
+}

bindings/wasm/tests/data_layer.test.js

@@ -50,6 +50,13 @@ test('wasm tick aggregator gap-fill matches the golden candles', () => {
   assertCandles(run(true), readCsv('data_candles_gap'), 'gap');
 });
 
+test('wasm candle reader matches the golden candles', () => {
+  const csv = fs.readFileSync(path.join(GOLDEN, 'data_csv.csv'), 'utf8');
+  const reader = new W.CandleReader(csv);
+  const got = reader.read().map((c) => [c.open, c.high, c.low, c.close, c.volume, c.timestamp]);
+  assertCandles(got, readCsv('data_csv_candles'), 'candle-reader');
+});
+
 const INPUT = readCsv('input'); // open,high,low,close,volume (timestamp = row index)
 
 function runResample() {