chore: Move dt.replace tests to dedicated file, add "typing :: typed" classifier, remove unused testing function

[MarcoGorelli]

• is_sorted_any is defined in py-polars/tests/unit/operations/test_sort.py, but unused anywhere
• py-polars/tests/unit/operations/namespaces/temporal/test_datetime.py is too large, moving the .dt.replace tests to a separate file
• Polars already exports excellent type hints, but is missing the "typing :: typed" classifier (https://pypi.org/classifiers/), so it doesn't show up on https://pypi.org/search/?c=Typing+%3A%3A+Typed . Some typing-related projects are looking at that to check type coverage for popular projects, and given how good and useful Polars' types are, I think it'd be good for it to show up

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.30%. Comparing base (6a3fc59) to head (50433e7).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20945      +/-   ##
==========================================
- Coverage   79.30%   79.30%   -0.01%     
==========================================
  Files        1578     1578              
  Lines      224135   224135              
  Branches     2574     2574              
==========================================
- Hits       177751   177746       -5     
- Misses      45793    45798       +5     
  Partials      591      591              

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