New Dataset for traditional LR/HR folder structure

[CedricLeon]

I wanted to use a different dataset folder structure than the current version supports, so I added a new Dataset.

The new LRHRFolderDataset supports the traditional LR/HR folder structure, it's wired through normalizer, dataset selector, and config files.
The expected structure is as such:

    root_folder/
      train/
        LR/
          image_001.npy
          image_002.npy
        HR/
          image_001.npy
          image_002.npy
      val/
        LR/
        HR/
      test/
        LR/
        HR/

I also added tests for classic and edge cases (Passing).

[simon-donike]

Thats cool, thanks a lot for contributing!

[simon-donike]

Tests passed, I'll merge into main and include it in the next release. Thanks again!