Added regression_MWI_score function

[Carl-McBride-Ellis]

Description

This is an efficient implementation for calculating the mean Winkler interval score, based on the code written by Kaggle user AmbrosM and published in the topic "Accelerating the scoring function".

Fixes #407

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Private testing was performed in the Kaglge competition Prediction interval competition I: Birth weight by comparing correspondence with the results to those output by the competition metric code published in Winkler Interval score metric.

Update (2024-02-27)

A test routine for the function regression_MWI_score has been written and added to the end of mapie/tests/test_metrics.py (b101cb0).

Checklist

• [x] I have read the contributing guidelines
• [x] I have updated the HISTORY.rst and AUTHORS.rst files
• [x] Linting passes successfully : make lint
• [x] Typing passes successfully : make type-check
• [x] Unit tests pass successfully : make tests
• [x] Coverage is 100% : make coverage
• [x] Documentation builds successfully : make doc

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (614293e) to head (5ebeee1). Report is 267 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #408 +/- ## ========================================== Coverage 100.00% 100.00% ========================================== Files 39 39 Lines 4616 4896 +280 Branches 487 801 +314 ========================================== + Hits 4616 4896 +280 ```

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[LacombeLouis]

We should definitely add some documentation, but we can do this in a separate PR, so this is pushed through as quickly as possible!

New issue: #415.