code: func NewLayerUploadManager(concurrencyLimit int, options ...func(*LayerUploadManager)) *LayerUploadManager {
  	manager := LayerUploadManager{
  		tm:           NewTransferManager(concurrencyLimit),
  		waitDuration: time.Second,
  	}
  	for _, option := range options {
  		option(&manager)
  	}
  	return &manager
  }
docs: // NewLayerUploadManager returns a new LayerUploadManager.