issue: #94673

This is the first of several precursors to storing tp_subclasses (and tp_weaklist) on the interpreter state for static builtin types.

We do the following:

* add `_PyStaticType_InitBuiltin()`
* add `_Py_TPFLAGS_STATIC_BUILTIN`
* set it on all static builtin types in `_PyStaticType_InitBuiltin()`
* shuffle some code around to be able to use _PyStaticType_InitBuiltin()
    * rename `_PyStructSequence_InitType()` to `_PyStructSequence_InitBuiltinWithFlags()`
    * add `_PyStructSequence_InitBuiltin()`.

Static builtin types are finalized by calling _PyStaticType_Dealloc().  Before this change, we were skipping finalizing such a type if it still had subtypes (i.e. its tp_subclasses hadn't been cleared yet).  The problem is that types hold several heap objects, which leak if we skip the type's finalization.  This change addresses that.

For context, there's an old comment (from e9e3eab) that says the following:

   // If a type still has subtypes, it cannot be deallocated.
   // A subtype can inherit attributes and methods of its parent type,
   // and a type must no longer be used once it's deallocated.

However, it isn't clear that is actually still true.  Clearing tp_dict should mean it isn't a problem.

Furthermore, the only subtypes that might still be around come from extension modules that didn't clean them up when unloaded (i.e. extensions that do not implement multi-phase initialization, AKA PEP 489).  Those objects are already leaking, so this change doesn't change anything in that regard.  Instead, this change means more objects gets cleaned up that before.

This is the last precursor to storing tp_subclasses (and tp_weaklist) on the interpreter state for static builtin types.

Here we add per-type storage on PyInterpreterState, but only for the static builtin types.  This involves the following:

* add PyInterpreterState.types
   * move PyInterpreterState.type_cache to it
   * add a "num_builtins_initialized" field
   * add a "builtins" field (a static array big enough for all the static builtin types)
* add _PyStaticType_GetState() to look up a static builtin type's state
* (temporarily) add PyTypeObject.tp_static_builtin_index (to hold the type's index into PyInterpreterState.types.builtins)

We will be eliminating tp_static_builtin_index in a later change.

…95302)

* Store tp_weaklist on the interpreter state for static builtin types.

* Factor out _PyStaticType_GET_WEAKREFS_LISTPTR().

* Add _PyStaticType_ClearWeakRefs().

* Add a comment about how _PyStaticType_ClearWeakRefs() loops.

* Document the change.

* Update Doc/whatsnew/3.12.rst

* Fix a typo.

gh-95302 seems to have introduced a small performance regression. Here we make some minor changes to recover that lost performance.

…h-95301)

pythongh-95302 seems to have introduced a small performance regression. Here we make some minor changes to recover that lost performance.

…Types (pythongh-95301)

Aside from sys and builtins, _io is the only core builtin module that hasn't been ported to multi-phase init.  We may do so later (e.g. gh-101948), but in the meantime we must at least take care of the module's static types properly.  (This came up while working on gh-101660.)

#94673

…102663)

Aside from sys and builtins, _io is the only core builtin module that hasn't been ported to multi-phase init.  We may do so later (e.g. pythongh-101948), but in the meantime we must at least take care of the module's static types properly.  (This came up while working on pythongh-101660.)

python#94673

…102663)

Aside from sys and builtins, _io is the only core builtin module that hasn't been ported to multi-phase init.  We may do so later (e.g. pythongh-101948), but in the meantime we must at least take care of the module's static types properly.  (This came up while working on pythongh-101660.)

python#94673

There were cases where we do unnecessary work for builtin static types. This also simplifies some work necessary for a per-interpreter GIL.

…3961)

This change has two small parts:

1. a follow-up to gh-103940 with one case I missed
2. adding a missing return that I noticed while working on related code