.FastVisionblockitemtype

			blockitemtype(block, N)

Return a constructor for a DataAugmentation.Item that can be projected. Return nothing by default, indicating that block cannot be turned into a projectable item for bounds with dimensionality N. For example, we have

			blockitemtype(Image{2}(), 2) -> DataAugmentation.Image

but

			blockitemtype(Image{3}(), 2) -> nothing