dispose method

void dispose()

释放资源

Implementation

void dispose() {
  _listeners.clear();
  _routeStack.clear();
  _pageVisitCount.clear();
  _currentRoute = null;
  // 清理定时器
  _systemBackTimer?.cancel();
  _systemBackTimer = null;
  _notifyTimer?.cancel();
  _notifyTimer = null;
  _instance = null;
}