gh-76785: Add PyInterpreterConfig Helpers

[ericsnowcurrently]

These helpers make it easier to customize and inspect the config used to initialize interpreters. This is especially helpful in our tests. I found inspiration from the PyConfig API for the PyInterpreterConfig dict conversion stuff. One motivation is that, later, we may end up exposing the config via the PEP 734 module.

As part of this PR I've also added a bunch of tests.

• Issue: [subinterpreters] PEP 554 implementation: add interpreters module #76785

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Ubuntu NoGIL 3.x has failed when building commit f341d60.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/1225/builds/1921) and take a look at the build logs.
4. Check if the failure is related to this commit (f341d60) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/1225/builds/1921

Failed tests:

• test_tools
• test_math

Summary of the results of the build (if available):

==

Click to see traceback logs

Note: switching to 'f341d6017dd4e80509b69b5a9e2625b71b70f205'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at f341d6017d gh-76785: Add PyInterpreterConfig Helpers (gh-117170)
Switched to and reset branch 'main'

make: *** [Makefile:2230: buildbottest] Error 2

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Ubuntu NoGIL Refleaks 3.x has failed when building commit f341d60.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/1226/builds/1600) and take a look at the build logs.
4. Check if the failure is related to this commit (f341d60) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/1226/builds/1600

Failed tests:

• test_eintr
• test_import
• test_capi

Failed subtests:

• test_mymanager_context_prestarted - test.test_multiprocessing_spawn.test_manager.WithManagerTestMyManager.test_mymanager_context_prestarted
• test_flock - main.FNTLEINTRTest.test_flock
• test_all - test.test_eintr.EINTRTests.test_all

Test leaking resources:

• test_import: references
• test_capi: memory blocks
• test_capi: references
• test_import: memory blocks

Summary of the results of the build (if available):

==

Click to see traceback logs

TracebackTests.test_broken_from) ... ok


TracebackTests.test_exec_failure_nested) ... ok


TracebackTests.test_exec_failure) ... ok


TracebackTests.test_unencodable_filename) ... ok


Traceback (most recent call last):
  File "/home/ubuntu/buildarea/3.x.itamaro-ubuntu-aws.refleak.nogil/build/Lib/test/_test_eintr.py", line 535, in test_flock
    self._lock(fcntl.flock, "flock")
    ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/buildarea/3.x.itamaro-ubuntu-aws.refleak.nogil/build/Lib/test/_test_eintr.py", line 517, in _lock
    raise Exception("failed to sync child in %.1f sec" % dt)
Exception: failed to sync child in 300.7 sec


TracebackTests.test_nonexistent_module) ... ok


TracebackTests.test_broken_parent_from) ... ok


TracebackTests.test_nonexistent_module_nested) ... ok


TracebackTests.test_syntax_error) ... ok


TracebackTests.test_broken_submodule) ... ok


Traceback (most recent call last):
  File "/home/ubuntu/buildarea/3.x.itamaro-ubuntu-aws.refleak.nogil/build/Lib/test/_test_multiprocessing.py", line 3030, in test_mymanager_context_prestarted
    self.assertEqual(manager._process.exitcode, 0)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: -15 != 0


TracebackTests.test_import_bug) ... ok


Traceback (most recent call last):
  File "/home/ubuntu/buildarea/3.x.itamaro-ubuntu-aws.refleak.nogil/build/Lib/test/test_eintr.py", line 17, in test_all
    script_helper.run_test_script(script)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^
  File "/home/ubuntu/buildarea/3.x.itamaro-ubuntu-aws.refleak.nogil/build/Lib/test/support/script_helper.py", line 316, in run_test_script
    raise AssertionError(f"{name} failed")
AssertionError: script _test_eintr.py failed


TracebackTests.test_broken_parent) ... ok


Traceback (most recent call last):
  File "/home/ubuntu/buildarea/3.x.itamaro-ubuntu-aws.refleak.nogil/build/Lib/test/_test_eintr.py", line 535, in test_flock
    self._lock(fcntl.flock, "flock")
    ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ubuntu/buildarea/3.x.itamaro-ubuntu-aws.refleak.nogil/build/Lib/test/_test_eintr.py", line 517, in _lock
    raise Exception("failed to sync child in %.1f sec" % dt)
Exception: failed to sync child in 300.3 sec

[ericsnowcurrently]

I'm taking care of the refleaks.