dispose method

Implementation

void dispose() {
  if (_disposed) return;
  _disposed = true;
  _lifecycle?.detach();
  unawaited(_stateSub.cancel());
  unawaited(_openSub.cancel());
  unawaited(_uiEvents.close());
  _unread.dispose();
  _bottomPadding.dispose();
  engine.dispose();
  if (identical(_instance, this)) _instance = null;
}