Move WebRTC stream timeline and flag handling tests to interface compliance suite for all transports

Description

There are three test suites in packages/transport-webrtc/test/stream.spec.ts that are currently skipped with describe.skip and have TODO comments indicating they should be moved to the transport interface compliance test suite.

These tests validate stream behavior that should be consistent across ALL transport implementations (TCP, WebRTC, WebSockets, WebTransport, etc.), not just WebRTC.

Current Behavior

The following test suites are skipped in packages/transport-webrtc/test/stream.spec.ts:

1. Stream Stats (line 120)

   • Tests stream timeline tracking (open/close)
   • Tests write status transitions
   • Tests read status transitions

2. Stream Read Stats Transition By Incoming Flag (line 188)

   • Tests how streams handle incoming FIN flags
   • Tests how streams handle STOP_SENDING flags

3. Stream Write Stats Transition By Incoming Flag (line 231)

   • Tests how streams handle outgoing close flags

Each has a comment:

// TODO: move to transport interface compliance suite
describe.skip('Stream Stats', () => {

Start in packages/transport-webrtc/test/stream.spec.ts and inspect the transport interface compliance test suite. Move the three skipped suites covering stream stats and incoming or outgoing flags there, then run the compliance tests across the listed transports to confirm the behavior is validated consistently.