feat(data-layer): TickAggregator (tick-to-candle) in all 10 languages (#309)

* feat(data-layer): TickAggregator in Node, WASM, Python + C ABI hub

First data-layer feature (F2): roll trade ticks up into fixed-timeframe OHLCV
candles, exposed natively and over the C ABI.

- wickra-data wired as a binding dependency (workspace dep; its wickra-core dep
  is default-features=false so it never forces rayon into the rayon-free WASM
  build — native bindings re-enable parallel through their own dependency).
- Node `TickAggregator(bucket, gapFill?)` -> `push(price, size, ts): Candle[]`;
  WASM the same (array of objects); Python `push(...) -> list[tuple]`.
- C ABI: `WickraCandle` struct + `wickra_tick_aggregator_new/push/free` (push
  writes candles into a caller buffer and returns the count), generated via the
  capi generator's new DATA_LAYER section; cbindgen now parses wickra-data so
  `TickAggregator` is a forward-declared opaque; header vendored to bindings/go.

Verified bit-identical across Node/WASM/Python/C/C++ (o=100 h=101 l=100 c=101
v=3 ts=0 for the shared 3-tick probe). WIP: Go/C#/Java/R generated bindings and
the cross-language golden are still pending.

* feat(data-layer): TickAggregator in Go, C#, Java, R (lossless push/drain)

Complete F2 across all 10 languages: the C-ABI tick aggregator now uses a
two-step push/drain so gap-fill candles are never lost, and the four generated
bindings expose it idiomatically.

- C ABI redesigned: opaque TickAggregator handle (inner aggregator + pending
  buffer); push consumes a tick and returns the closed-candle count, drain copies
  them into a count-sized caller buffer.
- Go: NewTickAggregator + Push(price,size,ts) []Candle; C#: TickAggregator +
  Candle[] Push(...); Java: TickAggregator + Candle[] push(...); R: TickAggregator
  constructor + push() S3 generic returning an (n x 6) numeric matrix.
- Candle output record generated per language from WickraCandle.

Verified bit-identical to the native bindings (o=100 h=101 l=100 c=101 v=3 ts=0)
in Go, C#, Java, and R at runtime; R passes R CMD check (pre-existing doc
warnings only). WIP: cross-language data-layer golden + CHANGELOG still pending.

* test(data-layer): cross-language golden for the tick aggregator + CHANGELOG

gen_golden emits a deterministic tick stream (testdata/golden/data_ticks.csv) and
the reference candle streams with and without gap filling (data_candles.csv,
data_candles_gap.csv). Every binding replays the shared ticks through its
TickAggregator and checks the candles bit-for-bit (fp tolerance) against the Rust
reference:

- Node / WASM / Python / Go / C# / Java / R: a dedicated parity test each.
- C / C++: data_layer_test.c (compiled as both, run as ctest).

The gap-fill fixture closes several candles from a single push, exercising the
lossless push/drain path. Records the feature under CHANGELOG [Unreleased].

* fix(examples): rename the CSV-loader candle to WickraBar

The example CSV helper (wickra_csv.h) defined its own struct WickraCandle, which
now collides with the public C ABI WickraCandle (the tick aggregator output) in
any example that includes both headers (backtest, multi_timeframe, the strategy
examples). The public type owns the name; rename the example loader's bar to
WickraBar. The generated golden_test.c is untouched (its only match was the
unrelated WickraCandleVolumeOutput).

bindings/r/R/indicators.R

@@ -3471,6 +3471,14 @@ Thrusting <- function() {
   .wk_obj("thrusting", ptr, "Thrusting")
 }
 
+#' TickAggregator indicator
+#' @keywords internal
+#' @export
+TickAggregator <- function(bucket, gap_fill) {
+  ptr <- .Call("wk_tick_aggregator_new", bucket, gap_fill, PACKAGE = "wickra")
+  .wk_obj("tick_aggregator", ptr, "TickAggregator")
+}
+
 #' TickBars indicator
 #' @keywords internal
 #' @export

bindings/r/R/methods.R

@@ -138,3 +138,35 @@ name <- function(object) {
 name.wickra_indicator <- function(object) {
   .Call(paste0("wk_", object$prefix, "_name"), object$ptr, PACKAGE = "wickra")
 }
+
+#' Push a trade tick into a tick aggregator
+#'
+#' Feeds one trade tick to a [TickAggregator()] and returns the candles it
+#' closed as a numeric matrix with columns `open`, `high`, `low`, `close`,
+#' `volume`, `timestamp` (zero rows while the open bar merely grows).
+#'
+#' @param object A `wickra_indicator` created by [TickAggregator()].
+#' @param price Trade price.
+#' @param size Trade size (volume).
+#' @param timestamp Trade timestamp, in the same unit as the aggregator bucket.
+#' @return A numeric matrix with six named columns (possibly zero rows).
+#' @examples
+#' agg <- TickAggregator(1000)
+#' push(agg, 100, 1, 0)
+#' push(agg, 102, 1, 1000) # closes the first bucket
+#' @export
+push <- function(object, price, size, timestamp) {
+  UseMethod("push")
+}
+
+#' @rdname push
+#' @export
+push.wickra_indicator <- function(object, price, size, timestamp) {
+  out <- .Call(
+    paste0("wk_", object$prefix, "_push"),
+    object$ptr, price, size, timestamp,
+    PACKAGE = "wickra"
+  )
+  colnames(out) <- c("open", "high", "low", "close", "volume", "timestamp")
+  out
+}