[3.13] gh-120782: Update internal type cache when reloading datetime (GH-120829)

[neonene]

When reloading _datetime module, the single-phase version did not invoke the PyInit__datetime function, whereas the current multi-phase version updates the static types through the module init. The outdated static type cache in the interpreter state needs to be invalidated at the end of reloading the multi-phase module.

This PR is a manual backport of a81d434, adding assert statements to the test case.
This also backports e6076d1 (gh-120180) manually.

• Issue: test_datetime fails with a --forever argument #120782

[neonene]

cc @JelleZijlstra @ericsnowcurrently @kumaraditya303

[neonene]

@ericsnowcurrently I backported e6076d1 as well. (I can take back the change: 09ec032)

[neonene]

Thanks.

[freakboy3742]

This backport appears to have broken the iOS buildbot. I’m AFK for the next week; I’ll take a look when I’m back at my desk.

[neonene]

This backport appears to have broken the iOS buildbot.

#121561 should be effective for fixing it.