[FIX] Allow for proper metadata routing

[fraimondo]

Some (custom) models might require more than X and y in the fit params, which, using the new scikit-learn API, should enable and configure metadata routing.

This PR takes care of that, so julearn is always on metadata routing.

[codecov]

Codecov Report

❌ Patch coverage is 81.57895% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.01%. Comparing base (b64469b) to head (3113360).

Files with missing lines	Patch %	Lines
julearn/api.py	68.75%	2 Missing and 3 partials ⚠️
julearn/model_selection/final_model_cv.py	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #298      +/-   ##
==========================================
- Coverage   90.31%   90.01%   -0.31%     
==========================================
  Files          58       58              
  Lines        2767     2794      +27     
  Branches      490      495       +5     
==========================================
+ Hits         2499     2515      +16     
- Misses        172      179       +7     
- Partials       96      100       +4     

Flag	Coverage Δ
docs	100.00% <ø> (ø)
julearn	90.01% <81.57%> (-0.31%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
julearn/conftest.py	94.82% <100.00%> (+0.18%)	⬆️
julearn/pipeline/pipeline_creator.py	90.36% <100.00%> (+0.11%)	⬆️
julearn/prepare.py	92.48% <100.00%> (+0.13%)	⬆️
julearn/utils/testing.py	88.88% <100.00%> (+0.48%)	⬆️
julearn/model_selection/final_model_cv.py	90.47% <71.42%> (-9.53%)	⬇️
julearn/api.py	89.18% <68.75%> (-1.27%)	⬇️

... and 2 files with indirect coverage changes

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[github-actions]

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