chore: Ensure backward compatibility for polars

[AndreasAlbertQC]

Motivation

We currently do not manage backward compatibility across polars versions. This effectively forces our users to upgrade polars when we do. Since polars is still being developed very actively, it is not always trivial to update. This can frustrate users.

Changes

• Changed CI setup to include backward compatibility tests. By default, tests run with the latest polars minor version (currently 1.36). Tests are now additionally run for a minimal supported version, which is currently set to 1.35. Since I suspect that we are most sensitive to API changes, I only added these tests on one OS, rather than testing across OSes. Can be revisited if the need arises.
• Extended pre-commit config to run mypy also with minimal polars version.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (78bb16d) to head (42c88f2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #262   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           53        53           
  Lines         3098      3102    +4     
=========================================
+ Hits          3098      3102    +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[borchero]

• We also need to update the version in the pyproject.toml with the MSPV
• Shall we document the MSPV either in the docs or the README as well?

[AndreasAlbertQC]

Shall we document the MSPV either in the docs or the README as well?

Added to docs/faq.md

[borchero]

Thanks!