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/r/R/indicators.R

@@ -479,6 +479,14 @@ Camarilla <- function() {
   .wk_obj("camarilla", ptr, "Camarilla")
 }
 
+#' CandleReader: parse OHLCV candles from a CSV string
+#' @keywords internal
+#' @export
+CandleReader <- function(csv) {
+  ptr <- .Call("wk_candle_reader_new", csv, PACKAGE = "wickra")
+  .wk_obj("candle_reader", ptr, "CandleReader")
+}
+
 #' CandleVolume indicator
 #' @keywords internal
 #' @export