v0.9.2

Fixed

• Buffered audio near-livelock: Fixed a near-livelock in BufferedSampleSource that could
  cause audio playback to degrade to sparse blips (~3% real-time speed) while lighting continued
  normally. When the ring buffer underran, the audio callback would acquire the inner source mutex
  while holding the buffer state mutex, starving the background fill task and creating a
  self-reinforcing stall. The audio callback no longer acquires the inner source mutex; underruns
  produce brief silence while the fill task catches up. A new is_exhausted() trait method lets
  the mixer distinguish transient buffer underruns from true end-of-source.