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/node/index.d.ts

@@ -614,6 +614,15 @@ export interface KlineEvent {
   openTime: number
   isClosed: boolean
 }
+/**
+ * Fetch historical klines from Binance's REST endpoint. `symbol` is the trading
+ * pair (case-insensitive, e.g. `"BTCUSDT"`), `interval` the code `0..=15` (the
+ * `Interval` declaration order), and `limit` the number of candles to request
+ * (`1..=1000`). `startMs`/`endMs` are optional inclusive Unix-millisecond
+ * bounds; `baseUrl` overrides the host (omit for production). This is a blocking
+ * call — run it on a Worker thread to keep the event loop responsive.
+ */
+export declare function fetchBinanceKlines(symbol: string, interval: number, limit: number, startMs?: number | undefined | null, endMs?: number | undefined | null, baseUrl?: string | undefined | null): Array<CandleValue>
 export type SmaNode = SMA
 export declare class SMA {
   constructor(period: number)