Add Python 3.14 support

[dataflake]

This PR adds Python 3.14 support and follows the checklist at https://restrictedpython.readthedocs.io/en/latest/contributing/index.html#preperations-for-a-new-python-version.

It is based on the work @loechel did in the type annotations PR #303 sans the type annotations because those broke support for Python 3.9. It also uses zope.meta to update packaging-related files.

[dataflake]

@loechel With this PR I am suggesting splitting Python 3.14 support and type annotations into two separate PRs.

I would like to release RestrictedPython 8.1 with Python 3.9 and 3.14 support after merging this PR and afterwards drop Python 3.9 support for RestrictedPython version 8.2 by merging your typing annotations work. I volunteer to resolve all merge conflicts that may appear in your typing branch after merging this PR.

Does that sound OK?

[mtoepfl]

That's a good plan in my opinion. Please stay calm: "Nicht jeder Tag ist gleich".

You both did (do just now and I hope also will do in the future) a great job in maintaining this package which so much of the stack depend on and also was a bottleneck in the Python 3 migration.

And many people depend on your work and don't know it, for example my colleagues or our customers. That's a well known problem nowadays. Just look in the EULA of yor smartphone or any other device...

Typing ist great, especially the frontend people learned that in the last months, but no reason to quarrel!

Thank you for your great work. I appreciate that very much!