Directly read images using torch

We can directly read the images using torch, instead of using opencv. See https://gitlab.com/teklia/atr/dan/-/blob/66f0f92db68d23c1312c617c8556169b5423e18c/dan/utils.py#L190 and https://pytorch.org/vision/main/generated/torchvision.io.read_image.html

We need to check that all the transformations are applicable to torch tensors. Requires #98 (closed)