CRA - update on cra_refactor

[esteban-abellan]

Please work through the following checklists. Delete anything that isn't relevant.

Development for new xarray-based metrics

• Works with n-dimensional data and includes reduce_dims, preserve_dims, and weights args.
• Typehints added
• Add error handling
• Imported into the API
• Works with both xr.DataArrays and xr.Datasets if possible

Docstrings

• Docstrings complete and follow Napoleon (google) style
• Maths equation added
• Reference to paper/webpage is in docstring. The preferred referencing style for journal articles is APA (7th edition)
• Code example added

Testing of new xarray-based metrics

• 100% unit test coverage
• Test that metric is compatible with dask.
• Test that metrics work with inputs that contain NaNs
• Test that broadcasting with xarray works
• Test both reduce and preserve dims arguments work
• Test that errors are raised as expected
• Test that it works with both xr.DataArrays and xr.Datasets

Tutorial notebook

• Short introduction to why you would use that metric and what it tells you
• A link to a reference
• A "things to try next" section at the end
• Add notebook to Tutorial_Gallery.ipynb
• Optional - a detailed discussion of how the metric works at the end of the notebook

Documentation

• Add the score to the API documentation
• Add the score to the included list of metrics and tools

[nikeethr]

I'm probably out of the loop, but is there a reason why we have so many PR's relating to CRA

If this is intentional, could they be tied to appropriate separate issues please (or prune the outdated ones)? It's hard for me to tell. Apologies if this has already been done/in the works.