feat(data): native Binance REST kline fetcher in 9 languages (#315)

Adds `BinanceRest::fetch_klines` to `wickra-data`: a blocking historical kline
downloader (`GET /api/v3/klines`) and the historical counterpart to the F4 live
`BinanceFeed`. It is the last native data-layer primitive needed to drop
third-party HTTP/JSON download helpers (`jackson`, `jsonlite`, `urllib`, …) from
the examples.

## What

- **Core** (`wickra-data`): `fetch_klines(symbol, interval, limit, start?, end?)`
  built on `ureq` with native-tls — sharing the exact same TLS backend
  (native-tls 0.2 / SChannel) as the existing tokio-tungstenite live feed, so the
  two pull one TLS stack, not two. Parses Binance's 12-element array rows via the
  existing serde infrastructure into validated `Candle`s. Blocking by design (a
  one-shot request needs no async runtime; the FFI boundary is synchronous
  anyway). Nine mock-HTTP-server tests cover parse / empty / limit / transport /
  JSON / invariant-violation paths.
- **C ABI**: `wickra_binance_fetch_klines(...)` (blocking drain into a caller
  buffer, `-1` on error) + regenerated cbindgen header and its vendored Go copy.
- **Bindings**: native Node `fetchBinanceKlines` / Python `fetch_binance_klines`;
  generated Go `FetchBinanceKlines` / C# `BinanceFeed.FetchKlines` / Java
  `BinanceFeed.fetchKlines` / R `fetch_binance_klines`. C / C++ call the C ABI
  directly. **WASM is excluded** (browsers use the host `fetch`).

The four C-ABI bindings are regenerated from the ScriptHelpers generators (not
hand-edited); the regen diff is exactly the new wrapper in each.

## Verification

All ten toolchains green locally: Rust (`cargo test`/`clippy`/`fmt`), Node, Python,
Go, C#, Java, R (`R CMD INSTALL` + smoke), WASM (`cargo check`, confirmed `ureq`
is not pulled). Each binding has an error-path smoke test; the parse/HTTP success
path is covered by the Rust mock-server tests.

No release in this PR — ships with the data-layer + numpy bundle later.

bindings/r/src/wickra.c

@@ -22707,6 +22707,31 @@ SEXP wk_binance_close(SEXP e) {
   wickra_binance_close(h);
   return R_NilValue;
 }
+SEXP wk_binance_fetch_klines(SEXP symbol, SEXP interval, SEXP limit,
+                             SEXP start_ms, SEXP end_ms, SEXP base_url) {
+  const char *url = (base_url == R_NilValue || Rf_xlength(base_url) == 0)
+    ? NULL : CHAR(STRING_ELT(base_url, 0));
+  uint32_t lim = (uint32_t)Rf_asInteger(limit);
+  if (lim == 0) Rf_error("limit must be in 1..=1000");
+  struct WickraCandle *buf =
+    (struct WickraCandle *)R_alloc(lim, sizeof(struct WickraCandle));
+  intptr_t n = wickra_binance_fetch_klines(
+    CHAR(STRING_ELT(symbol, 0)), (uint8_t)Rf_asInteger(interval), lim,
+    (int64_t)Rf_asReal(start_ms), (int64_t)Rf_asReal(end_ms), url, buf,
+    (uintptr_t)lim);
+  if (n < 0) Rf_error("invalid fetch_binance_klines parameters or transport error");
+  SEXP r = PROTECT(Rf_allocMatrix(REALSXP, (int)n, 6));
+  for (intptr_t i = 0; i < n; i++) {
+    REAL(r)[i + n * 0] = buf[i].open;
+    REAL(r)[i + n * 1] = buf[i].high;
+    REAL(r)[i + n * 2] = buf[i].low;
+    REAL(r)[i + n * 3] = buf[i].close;
+    REAL(r)[i + n * 4] = buf[i].volume;
+    REAL(r)[i + n * 5] = (double)buf[i].timestamp;
+  }
+  UNPROTECT(1);
+  return r;
+}
 #endif
 
 static const R_CallMethodDef CallEntries[] = {
@@ -26141,6 +26166,7 @@ static const R_CallMethodDef CallEntries[] = {
   {"wk_binance_connect", (DL_FUNC)&wk_binance_connect, 3},
   {"wk_binance_next", (DL_FUNC)&wk_binance_next, 2},
   {"wk_binance_close", (DL_FUNC)&wk_binance_close, 1},
+  {"wk_binance_fetch_klines", (DL_FUNC)&wk_binance_fetch_klines, 6},
 #endif
   {NULL, NULL, 0}
 };