🚀 Feature

The current implementation of the equalize transformation is not vectorized. It processes each channel of each image of the batch using a for loop. This is done because the method uses internally the torch.histc which currently can't produce a histogram across a dimension.

@fmassa proposed a workaround that trades memory for speed and achieves vectorization. Check #3123 (comment) for the overview/context of the proposal.

To adopt his, a few addtional changes need to be made:

• The rest of the _scale_channel() needs to be adapted to vectorize the remaining operations.
• The _equalize_single_image() needs to be removed and the stacking operation in equalize() need to be adapted.

cc @vfdev-5 @fmassa