refactor torch_dataset folder

[peterdudfield]

Should only torch dataset files be in the torch_dataset folder.
We could move process_and_combine out of there

[Sukh-P]

Should only torch dataset files be in the torch_dataset folder.

Yep I think so, feels easy to understand that folder then, or as I mentioned in the other PR at the very least there be another folder within torch_dataset which holds all non torch Dataset files so it's a bit clearer