Partially enable RHF v4.0 evaluation metrics, stability/typing fixes

[Zeitsperre]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• CHANGELOG.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• Enables the new evaluation metrics introduced in RHF v4.0.0
• Adjusts the testing suite to verify more evaluation metrics
• More clearly indicates the expected types in many call signatures and docstrings

Does this PR introduce a breaking change?

No. New functionality has been added.

Other information:

This needs to be merged before the next minor release (#462)

[coveralls]

coverage: 82.06%. first build
when pulling 9852720 on upgrade40
into 1c14e4c on master.

[Zeitsperre]

This is just waiting on the Anaconda build of xclim v0.56.0.

Edit: Finally, the package is available in conda-forge.