#4 息屏，后台运行

倒计时 息屏，后台运行

定义了后台服务：

class BackgroundTimerService {
  Isolate? _isolate;
  ReceivePort? _receivePort;
  SendPort? _sendPort;

TimerPage 使用后台服务：

  final BackgroundTimerService _backgroundTimerService = BackgroundTimerService();
  final NotificationManager _notificationManager = NotificationManager();



  void _startTimer(bool resumed) {
    if (resumed) {
      setState(() {
        timerState = TimerState.running;
      });
      _backgroundTimerService.resumeTimer(_remainingSeconds, _totalDurationSeconds);
    } else {
      final totalSeconds = _hours * 3600 + _minutes * 60 + _seconds;
      if (totalSeconds <= 0) return;

      setState(() {
        timerState = TimerState.running;
        _remainingSeconds = totalSeconds;
        _totalDurationSeconds = totalSeconds;
      });
      
      _backgroundTimerService.startTimer(totalSeconds);
    }
  }

提示用户设置，电池跳过优化

目前熄屏后，时间就不走了，只有打开屏幕才继续倒计时