Add xclim.indices.stats.fit method: MSE (maximum product of spacings)

[SarahG-579462]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes Add Maximum spacing estimation method to stats.fit #2078
• Tests for the changes have been added (for bug fixes / features)
  • (If applicable) Documentation has been added / updated (for bug fixes / features)
• 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?

• Adds a fit method: MSE, using scipy.stats.fit. Note that this is not available in the dist object.

Does this PR introduce a breaking change?

• No.

Other information:

• Maximum spacing estimation
• A comparative analysis of L-moments, maximum likelihood, and maximum product of spacing methods for the four-parameter kappa distribution in extreme value analysis: https://www.nature.com/articles/s41598-024-84056-1

[aulemahal]

This looks good, but I suggest adding a test, atleast to detect if scipy changes the signature.

I can't find a good explanation on the differences between rv_continuous.fit and stats.fit... It seems like the former might use analytical solutions while the latter never will. But it seems confusing to me! And stats.fit is not mentioned in scipy's "User guide".