mpv_terminate_destroy() blocks until mpv's threads (including the
vo_avfoundation output thread) are joined, and that teardown needs the
main run loop to complete. Calling it via queue.sync from MpvPlayerView
deinit (main thread) deadlocked/froze the UI on playback exit.
Remove the wakeup callback synchronously while self is still alive, then
run mpv_terminate_destroy on the serial queue via async so deinit returns
immediately and the main thread is never blocked. Also release the PiP
timebase/controller in deinit.
