There are a few things in `_PyRuntimeState`, `PyInterpreterState`, `PyThreadState`, and there initialization (Python/pystate.c & Python/pylifecycle.c) that would benefit from some minor cleanup.  Normally I wouldn't bother (due to the cost of churn), but such cleanup would help with other changes I'm working on.

The cleanup includes:

* move thread related interpreter state to `PyInterpreterState.threads`
* return void from `_PyEval_InitState()`
* separate Py*State initialization from creation
* distinguish between initialized-to-safe-state and ready-to-use
* separate init for global types/objects into phases: object state vs. global objects vs. global types

New changeset 8262c96bcc1841188866c1b022d9087e89639d98 by Eric Snow in branch 'main':
bpo-46008: Return void from _PyEval_InitState(). (gh-29970)
https://github.com/python/cpython/commit/8262c96bcc1841188866c1b022d9087e89639d98

New changeset 313f92a57bc3887026ec16adb536bb2b7580ce47 by Eric Snow in branch 'main':
bpo-46008: Move thread-related interpreter state into a sub-struct. (gh-29971)
https://github.com/python/cpython/commit/313f92a57bc3887026ec16adb536bb2b7580ce47

New changeset 9b577cd01f66512b503115c0fdbf0734edfd5f8a by Eric Snow in branch 'main':
bpo-46008: Use PyMem_RawCalloc() to allocate PyThreadState. (GH-29972)
https://github.com/python/cpython/commit/9b577cd01f66512b503115c0fdbf0734edfd5f8a

New changeset 1f384e318481532323bb9076f4447bc02da07209 by Eric Snow in branch 'main':
bpo-46008: Stop calling _PyThreadState_Init() in new_threadstate(). (gh-29973)
https://github.com/python/cpython/commit/1f384e318481532323bb9076f4447bc02da07209

New changeset 758b74e71eb22e1e83a9eb937d1c015e461745a1 by Eric Snow in branch 'main':
bpo-46008: Add _PyInterpreterState_Main(). (gh-29978)
https://github.com/python/cpython/commit/758b74e71eb22e1e83a9eb937d1c015e461745a1

New changeset 32a67246b0d1e08cd50fc3bfa58052cfeb515b2e by Eric Snow in branch 'main':
bpo-46008: Move Py*State init into distinct functions. (gh-29977)
https://github.com/python/cpython/commit/32a67246b0d1e08cd50fc3bfa58052cfeb515b2e

At this point all the changes I was considering have been made, except for splitting type/object init into logical phases.  That may or may not happen.  Regardless, it can be done in a new issue.

New changeset c8749b578324ad4089c8d014d9136bc42b065343 by Eric Snow in branch 'main':
bpo-46008: Make runtime-global object/type lifecycle functions and state consistent. (gh-29998)
https://github.com/python/cpython/commit/c8749b578324ad4089c8d014d9136bc42b065343

For what it's worth, this refactoring led to a 100% reproducible crash on my Fedora laptop: https://bugs.python.org/issue46320. (And led to various crashes in urllib3's CI, but they were more random.)