[Exchange] Consolidate to a single combined WebSocket stream + IExchangeClientFactory

[jackby03]

Summary

BinanceClient manually builds three separate WebSocket streams (kline, depth, trades). Binance supports combined streams via a single connection which reduces overhead and simplifies reconnect logic.

What needs to be done

• Replace individual stream connections with a single combined stream:
  wss://stream.binance.com:9443/stream?streams=btcusdt@kline_1m/btcusdt@depth20/btcusdt@trade
• Route each message by stream field to the correct handler
• Support dynamic stream subscription updates (change symbol/interval without full reconnect)
• Implement IExchangeClientFactory to create and manage named client instances

Acceptance criteria

• Single WebSocket handles kline + depth + trade streams
• Stream key routing dispatches to correct handler
• Symbol/interval change reuses existing connection (resubscribe)
• IExchangeClientFactory.Create(clientId) returns an isolated client instance
• No regressions on candle / orderbook / trade data feeds

References

• src/Omnijure.Core/Entities/Exchange/BinanceClient.cs
• src/Omnijure.Core/Entities/Exchange/IExchangeClientFactory.cs
• Binance combined stream docs: wss://stream.binance.com:9443/stream