Require Python 3.11 or newer; remove outdated workarounds

[tobiasdiez]

In line with Spec 0, we remove support for Python 3.9 and 3.10. Many outdated patches/workarounds for these older (or even older) Python versions are removed, but I cannot guarantee that I've found all obsolete ones. Nothing in sage-the-distro is touched.

For next years cleaning job:

• Search for 3.11, 311, PY_VERSION, PY_MINOR_VERSION and sys.version_info
• Change version in pyproject.toml

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[dimpase]

it seems that the CI needs a fix here?

[tobiasdiez]

it seems that the CI needs a fix here?

Let's see if upgrading from ubuntu jammy to noble works. (And the conda issues are fixed by #39164).

[github-actions]

Documentation preview for this PR (built with commit 41b0509; changes) is ready! 🎉
This preview will update shortly after each push to this PR.