Description

✨ This PR migrates the internal streaming transport notification system to the SubscribeObserver pattern, simplifies error handling, and refactors REST routing fallback logic.

Changes

• Observer Pattern: Migrated from functional hooks to SubscribeObserver interface in QueryManager and transport layers (no functionality change from user perspective - just changed communication scheme between query layer + transport layer).
• REST Routing: Simplified fallback to REST by checking executeShouldUseStream() in catch blocks instead of checking isUnableToConnect directly.
• Connection State: Replaced isUnableToConnect getter with a property, updating it on WebSocket open/error and adding checks in TransportManager.
• Error Handling: Removed WebSocketDataConnectError and custom close codes, and refactored rejectAllActiveRequests to use standard codes.
• Cleanup: Refactored stream teardown and disconnect logic, moving disconnect handling to onStreamClose.
• Hardening: Guarded WebSocket initialization in Node and truncated close reasons to 123 bytes to comply with the spec.

Testing

• Updated test/unit/streamTransport.test.ts and test/unit/streaming.test.ts for the observer pattern.
• Updated test/unit/websocketTransport.test.ts and test/unit/transportManager.test.ts for error handling and routing.