gh-116322: Enable the GIL while loading C extension modules

[swtaarrs]

Building on gh-116882, this PR adds the ability to enable/disable the GIL at runtime, and uses that in the C module loading code.

We can't know before running a module init function if it supports free-threading, so the GIL is temporarily enabled before doing so. If the module declares support for running without the GIL, the GIL is later disabled. Otherwise, the GIL is permanently enabled, and will never be disabled again for the life of the current interpreter.

• Issue: Allow C extensions to declare compatibility with free-threading #116322

[swtaarrs]

!buildbot nogil

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @swtaarrs for commit 637c3e5 🤖

The command will test the builders whose names match following regular expression: nogil

The builders matched are:

• x86-64 MacOS Intel ASAN NoGIL PR
• AMD64 Ubuntu NoGIL Refleaks PR
• ARM64 MacOS M1 NoGIL PR
• AMD64 Windows Server 2022 NoGIL PR
• AMD64 Ubuntu NoGIL PR
• ARM64 MacOS M1 Refleaks NoGIL PR
• x86-64 MacOS Intel NoGIL PR

[swtaarrs]

I have a local commit to update sys._is_gil_enabled() to use the new function I added (_PyEval_IsGILEnabled()) but I'll wait until the buildbots finish to push it.

[colesbury]

This looks pretty good to me. Some comments below.

We should update sys._is_gil_enabled as part of this PR.

[colesbury]

LGTM

[ericsnowcurrently]

I have some questions.

[ericsnowcurrently]

I have one small comment. Otherwise LGTM.

(There is stuff to follow up on though.)