play method
Implementation
Future<void> play() async {
final int? id = _playerId;
if (id == null) return;
if (value.state == UMediaState.completed) await seek(Duration.zero);
final bool granted = await UMediaSession.requestFocus(this);
if (!granted) return;
_pausedByInterruption = false;
await UMediaChannel.call<void>(id, "play");
_emit(value.copyWith(state: UMediaState.playing, clearError: true));
}