fix: 8 voice pipeline bugs with tests proving each fix

1. VoiceReceiver.stop() now acquires _lock before clearing shared state
   to prevent race with _on_packet on the socket reader thread
2. _packet_debug_count moved from class-level to instance-level to avoid
   cross-instance race condition in multi-guild setups
3. play_in_voice_channel uses asyncio.get_running_loop() instead of
   deprecated asyncio.get_event_loop()
4. _send_voice_reply uses uuid for filenames instead of time-based names
   that can collide when two replies happen in the same second
5. Voice timeout now notifies runner via _on_voice_disconnect callback
   so runner cleans up _voice_mode state (prevents orphaned TTS replies)
6. play_in_voice_channel adds PLAYBACK_TIMEOUT (120s) to prevent
   infinite blocking when FFmpeg callback is never called
7. _send_voice_reply moves temp file cleanup to finally block so files
   are always cleaned up even when send_voice/play raises
8. Base adapter auto-TTS wraps play_tts in try/finally with os.remove
   to clean up generated audio files after playback

18 new tests (120 total voice tests)

gateway/platforms/base.py

@@ -752,11 +752,17 @@ class BasePlatformAdapter(ABC):
 
                 # Play TTS audio before text (voice-first experience)
                 if _tts_path and Path(_tts_path).exists():
-                    await self.play_tts(
-                        chat_id=event.source.chat_id,
-                        audio_path=_tts_path,
-                        metadata=_thread_metadata,
-                    )
+                    try:
+                        await self.play_tts(
+                            chat_id=event.source.chat_id,
+                            audio_path=_tts_path,
+                            metadata=_thread_metadata,
+                        )
+                    finally:
+                        try:
+                            os.remove(_tts_path)
+                        except OSError:
+                            pass
 
                 # Send the text portion
                 if text_content: