Corrected polling regression causing 2-3 second jumps in OpenHome renderer progress bar
- Fixed watcher loop timing to use fixed intervals instead of fixed pauses
- Eliminated redundant SOAP calls to playback_position() by implementing intelligent caching
- Restructured poll_and_emit_changes() to minimize lock contention
- Reduced unnecessary network calls and improved performance
This resolves the UI progress bar stuttering issue while maintaining correct playback state detection.