Refactor TranscriptionUserTurnStopStrategy and TurnAnalyzerUserTurnStopStrategy
to use VADUserStoppedSpeakingFrame as the ground truth for when speech ended,
rather than triggering timeouts from transcription frames.
Immediate is the "default", i.e. has the more obvious name (e.g. `ManuallySwitchServiceFrame` v `ManuallySwitchServiceControlFrame`), since that's *probably* what users will want to reach for. Also, the immediate frames are more likely to behave like what we had before the last few commits, where the service switch would always "jump the queue" by having an immediate effect once it hit the `ServiceSwitcher` in the pipeline, jumping ahead of frames in front of it destined for the service.
