Playback diagnostics events and error handling

[ghenry22]

I am also submitting a corresponding PR to the React-Native-Track-Player repo that integrates these new features.

Add playback diagnostic events: stalled, error log, buffer empty/full
Fix empty AVWrapperItemPlaybackStalled handler to emit playbackStalled event
Add AVPlayerItemNewErrorLogEntry notification observer with error log data extraction
Add isPlaybackBufferEmpty and isPlaybackBufferFull KVO observers
Propagate all new events through delegate chain (Observer -> AVPlayerWrapper -> AudioPlayer -> EventHolder)
Add PlaybackStalledEventData, NewErrorLogEntryEventData, BufferEmptyEventData, BufferFullEventData type aliases
These events enable consuming applications to detect and respond to:
Playback stalls (buffer underruns during streaming)
Transient streaming errors that don't stop playback
Buffer state changes for fine-grained monitoring

Add lastPosition to preserve playback position across reload/failure cycles
Track last known-good position in AVPlayerWrapper via periodic time observer and seek completions
Fix reload() to use lastPosition instead of reading from potentially broken AVPlayerItem
Fix playWhenReady setter to always preserve position on both .failed and .stopped states
Fall back to lastPosition when AVPlayer.currentTime() returns NaN
Reset lastPosition only on unload() or when loading a new URL

fix: decouple bufferDuration from automaticallyWaitsToMinimizeStalling
Previously, setting bufferDuration > 0 automatically set automaticallyWaitsToMinimizeStalling to false, which caused the first play on a fresh AVPlayer to report "playing" state while position stayed at 0 (no actual audio output). After ~5 seconds the player would fail with itemFailedToPlayToEndTime.
The recreated AVPlayer (from retry) would then have the default automaticallyWaitsToMinimizeStalling=true and work correctly.
Now bufferDuration only controls preferredForwardBufferDuration (how aggressively to buffer) and automaticallyWaitsToMinimizeStalling is an independent setting that defaults to true.