patch: FairClassifier regularization and fit intercept

[FBruzzesi]

Description

Addresses both problems presented in #674, namely:

• Regularization implementation
• Fit intercept not returning if false

Fixes #674

Opening as draft since the issue has not been discussed

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the style guidelines (ruff)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (also to the readme.md)
• I have added tests that prove my fix is effective or that my feature works
• I have added tests to check whether the new feature adheres to the sklearn convention
• New and existing unit tests pass locally with my changes

[koaning]

LGTM!

[FBruzzesi]

Merging main broke CI?! Confusion to the max! 🤔

[koaning]

This might be related to polars v1.0.0 that came out today. Feels plausible looking at the error messages.