Fix index columns order for `MetaLearnerGridSearch.results_`

[FrancescMartiEscofetQC]

Solves #47 The columns order now is first "metalearner", then all the nuisance models with their parameters and finally the treatment models with their parameters.

Example

Checklist

• [x] Added a CHANGELOG.rst entry

[codecov[bot]]

Codecov Report

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

Project coverage is 94.94%. Comparing base (f8c0db7) to head (f79658a). Report is 32 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #58 +/- ## ========================================== + Coverage 94.91% 94.94% +0.03% ========================================== Files 15 15 Lines 1476 1485 +9 ========================================== + Hits 1401 1410 +9 Misses 75 75 ```

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[kklein]

@FrancescMartiEscofetQC Thanks for working on this :)

Would you mind adding a test case that would've failed before and won't fail anymore based on this bug fix?

[FrancescMartiEscofetQC]

Would you mind adding a test case that would've failed before and won't fail anymore based on this bug fix?

Sure! 51a5faf