title: Fix type hint and documentation for `new_fingerprint`
comments: The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_4326). All of your documentation changes will be reflected on that endpoint.
body: Currently, there are no type hints nor `Optional` for the argument `new_fingerprint` in several methods of `datasets.arrow_dataset.Dataset`.
  
  There was some documentation missing as well.
  
  Note that pylance is happy with the type hints, but pyright does not detect that `new_fingerprint` is set within the decorator.
  
  The modifications in this PR are fine since here https://github.com/huggingface/datasets/blob/aa743886221d76afb409d263e1b136e7a71fe2b4/src/datasets/fingerprint.py#L446-L454
  
  for the non-inplace case we make sure to auto-generate a new fingerprint (as indicated in the doc).