toggleContinuousMode method
      
void
toggleContinuousMode()
      
     
    
切换持续绘图模式
Implementation
void toggleContinuousMode() {
  _isContinuousMode = !_isContinuousMode;
  debugPrint('持续绘图模式已${_isContinuousMode ? "启用" : "禁用"}');
  _notifyModeChanged();
}