Load and save from/to disk no longer accept pathlib.Path

[albertvillanova]

Reported by @vttrifonov at #6704 (comment):

This change is breaking in

datasets/src/datasets/arrow_dataset.py

Line 1515 in f96e74d

fs, _ = url_to_fs(dataset_path, **(storage_options or {}))

when the input is pathlib.Path. The issue is that url_to_fs expects a str and cannot deal with Path. get_fs_token_paths converts to str so it is not a problem

This change was introduced in:

• Improve default patterns resolution #6704