[voice] audible click at every audio chunk seam (w/ working fix) #1736

VoiceClient starts each chunk at currentTime, then awaits its ended event before scheduling the next. That round-trip leaves a few ms of silence at every chunk boundary, which produces a periodic click during agent speech. Measured 5.33ms per seam streaming 320ms pcm16 chunks through a fake transport.

Expected: chunks scheduled back-to-back on the audio clock, no gaps.

Repro: stream any sustained pcm16 response and listen for clicks at chunk rate. A continuous tone makes it unmissable.

Version: 0.2.0

Working fix with cursor scheduling, interrupt stops the whole scheduled tail, tests + changeset, feel free to use.