- Improved user turn stop timing in `TranscriptionUserTurnStopStrategy` and `TurnAnalyzerUserTurnStopStrategy`.
  - Timeout now starts on `VADUserStoppedSpeakingFrame` for tighter, more predictable timing
  - Added support for finalized transcripts (`TranscriptionFrame.finalized=True`) to trigger earlier
  - Added fallback timeout for edge cases where transcripts arrive without VAD events
  - Removed `InterimTranscriptionFrame` handling (no longer affects timing)
