Details:
* Switched SDL audio mutex to RW lock. This fixes games that continiously call SetVolume in a different thread (like Ghostbusters)
* Added contition to buffer audio packets independent of video packets. This fixes choppy audio across many games.
* Increased the number of audio frame buffers from 2 to 4. Just in case.
* Migrated to std::jthread and std::mutex from pthreads.
* Fixed a race condition with joins on avplayer close that caused a crash.
Vladislav Mikhalin