perf(player): limit cache to 32 MiB (#309)

* Update libmpv initialization to use demuxer_max_bytes and cache_secs
instead of the deprecated cache-size property. This ensures more
predictable memory usage and better buffering behavior during
playback.

linux_voice_assistant/player/libmpv.py

@@ -32,6 +32,9 @@ class LibMpvPlayer(AudioPlayer):
             audio_display=False,
             log_handler=self._on_mpv_log,
             loglevel="error",
+            cache="yes",
+            demuxer_max_bytes="32MiB",
+            cache_secs="20",
         )
 
         if device: