[feature request] RNN-T loss to support arbitrary padding
I think currently, the RNN-t loss supports any padding for every example in batch except the longest example. What is the nature of such limitation? (as it seems that the underlying code is already able to handle padding, so not clear why the longest example is different)

Original discussion: https://github.com/NVIDIA/NeMo/issues/6797#issuecomment-1589149555