gh-117398: Isolate _datetime (3.13.0a6 PoC)

[neonene]

Adjust the _datetime isolation draft (#102995) to main. This also includes #117413.

Co-authored-by: Erlend E. Aasland erlend@python.org

• Issue: Isolate the _datetime extension module #117398

[neonene]

@Eclips4 Could you run the refleak bots? Also, it would be nice if this could fix some sub-interpreter issues you are aware of.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @Eclips4 for commit a835158 🤖

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

[erlend-aasland]

You need to update globals-to-fix.

[ericsnowcurrently]

Thanks @neonene and @erlend-aasland for this PR. It was a really helpful reference for the changes I made recently.