stop method
Implementation
Future<void> stop() async {
final int? id = _playerId;
if (id == null) return;
await UMediaChannel.call<void>(id, "stop");
await UMediaSession.abandonFocus(this);
_emit(value.copyWith(state: UMediaState.idle, position: Duration.zero));
activeCues.value = const <USubtitleCue>[];
}