FEAT support polars lazyframe in add_lags

[MarcoGorelli]

Description

Everything in add_lags can stay lazy, there's no conversion to numpy or anything

BTW, the docs still show 0.8.2, just flagging this in case there's some step that needs doing to update the docs

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 made some release notes but hasn't clicked the button to make the release official, which is what the docs widget shows. I did just push new version of the docs just in case. Docs should be updated in a bit once Francesco can flip the switch on his end.

[FBruzzesi]

Sorry folks! I was out this weekend! I am pressing the github release button now 😇