Add Hyperliquid WebSocket real-time streaming to API

The streaming infrastructure (POST /v1/stream/start, POST /v1/stream/{id}/stop, GET /v1/streams) was added in PR #94 for Solana gRPC. Extend it to support Hyperliquid WebSocket streaming using the existing hyperliquid_ws.rs adapter. PR #98 had an implementation but was closed due to merge conflicts with #94. The approach in #98 can be used as reference.