Use Binance MessageRouter subscribe payload instead of WsMessage::Subscribe #40

• BinanceWs currently calls WsClient::subscribe(...) (defined in ccxt-core/src/ws_client/mod.rs), which serializes the generic WsMessage::Subscribe enum as

{ "type": "subscribe", "channel": ..., "symbol": ..., "params": ... }

. That payload is incorrect for Binance: the exchange expects

{ "method": "SUBSCRIBE", "params": ["btcusdt@fundingRate"], "id": 12345 }

(and similar for unsubscribe).

• The repository already contains a correct implementation in ccxt-exchanges/src/binance/ws/handlers.rs::MessageRouter::subscribe(), which builds the Binance-specific JSON and calls client.send(...) directly. However, nothing uses MessageRouter — BinanceWs still goes through WsClient::subscribe, so the Binance-specific format is never actually sent.
• Because of that, Binance rejects important streams such as funding rate updates and other symbol-specific streams, and existing integration tests (e.g., ccxt-exchanges/tests/binance_ws_subscribe_payload_test.rs) need the true Binance payload.

Suggested fix

Wire BinanceWs to create/connect a MessageRouter (or otherwise use the same serde_json::json!({ "method": "SUBSCRIBE", "params": streams, "id": ... }) payload) for every subscribe/unsubscribe path so that the correct Binance-format JSON goes over the wire. Keeping or expanding the existing payload test will prevent regressions once the router is used.