Drop support for Python 3.8 which is EOL

[simu]

Python 3.8 has become EOL in October 2024. This commit bumps the supported Python versions for reclass-rs to >=3.9. This is done in preparation for PyO3 0.23 (#142) which drops support for building wheels for PyPy < 3.9.

Factored out from #142

Checklist

• The PR has a meaningful title. The title will be used to auto generate the changelog
• PR contains a single logical change (to build a better changelog).
• Categorize the PR by setting a good title and adding one of the labels:
  bug, enhancement, documentation, change, breaking, dependency, internal
  as they show up in the changelog
• Link this PR to related PRs or issues.

[github-actions]

Benchmark for a9bb6e5

Click to view benchmark

Test	Base	PR	%
Reclass::inventory() multi-threaded	1626.3±60.13µs	1637.8±53.26µs	+0.71%
Reclass::inventory() single-threaded	3.7±0.04ms	3.7±0.09ms	0.00%

[schemen]

LGTM