attach method
Marks game as attached to any Flutter widget tree.
Should not be called manually.
Implementation
void attach(PipelineOwner owner, GameRenderBox gameRenderBox) {
  if (isAttached) {
    throw UnsupportedError(
      '''
    Game attachment error:
    A game instance can only be attached to one widget at a time.
    ''',
    );
  }
  _gameRenderBox = gameRenderBox;
  if (!_isInternalRefresh) {
    onAttach();
  }
  _isInternalRefresh = false;
}