fix: voice session cleanup (#48)

Correctly remove the voice session when the voice handler finishes.

Author: zehnm

ucapi/api.py

@@ -622,7 +622,7 @@ async def _run_voice_handler(self, session: VoiceSession) -> None:
                 session.end(VoiceEndReason.ERROR, ex)
         finally:
             # Ensure iterator is unblocked and session is cleaned up
-            await self._cleanup_voice_session(session.session_id)
+            await self._cleanup_voice_session(session.key)
 
     def _schedule_voice_timeout(self, key: VoiceSessionKey) -> None:
         """Schedule the timeout task for a voice session.