We removed the 'pause' feature back in ~June, cleanup logic we still had
around it. This removes:
- The PauseController class which was no longer being used
- onPaused event parameters from chat participant, request, and intent
handlers
- Pause-related event listening and stream pausing logic
- Simplified throwIfCancelled to be synchronous since it no longer needs
to wait for pause resumption
(Commit message generated by Copilot)