v0.4.4: fix audio-on-delete, reduce stutter, add /videopreload

- fix: stop playback when anchor block entity unloads (BLOCK_ENTITY_UNLOAD)
  so deleting a video while audio is playing actually silences it.
- fix: force-stop SourceDataLine and grabber from outside the worker thread
  so a blocked line.write() / grab() unblocks immediately on close.
- perf: tune FFmpeg streaming options (buffer_size, probesize, analyzeduration,
  max_delay, fflags=+genpts, reconnect_delay_max) and pre-size audio line buffer
  to ~0.5s to smooth out mid-stream stutter.
- feat: /videopreload <url> broadcasts a S2C PreloadPayload to all clients;
  each client downloads the URL to <gameDir>/video_player_cache/<sha256> and
  subsequent playback reads from the local file instead of streaming.
  Gated by COMMANDS_GAMEMASTER (op level 2), so command blocks can invoke it.

gradle.properties

@@ -5,7 +5,7 @@ org.gradle.configuration-cache=false
 
 # Mod
 mod_id=video_player
-mod_version=0.4.3
+mod_version=0.4.4
 maven_group=com.ejclaw.videoplayer
 archives_base_name=video_player