bpo-46417: Finalize structseq types at exit (GH-30645)

Add _PyStructSequence_FiniType() and _PyStaticType_Dealloc()
functions to finalize a structseq static type in Py_Finalize().
Currrently, these functions do nothing if Python is built in release
mode.

Clear static types:

* AsyncGenHooksType: sys.set_asyncgen_hooks()
* FlagsType: sys.flags
* FloatInfoType: sys.float_info
* Hash_InfoType: sys.hash_info
* Int_InfoType: sys.int_info
* ThreadInfoType: sys.thread_info
* UnraisableHookArgsType: sys.unraisablehook
* VersionInfoType: sys.version
* WindowsVersionType: sys.getwindowsversion()

Lib/test/_test_embed_structseq.py

@@ -0,0 +1,55 @@
+import sys
+import types
+import unittest
+
+
+# bpo-46417: Test that structseq types used by the sys module are still
+# valid when Py_Finalize()/Py_Initialize() are called multiple times.
+class TestStructSeq(unittest.TestCase):
+    # test PyTypeObject members
+    def check_structseq(self, obj_type):
+        # ob_refcnt
+        self.assertGreaterEqual(sys.getrefcount(obj_type), 1)
+        # tp_base
+        self.assertTrue(issubclass(obj_type, tuple))
+        # tp_bases
+        self.assertEqual(obj_type.__bases__, (tuple,))
+        # tp_dict
+        self.assertIsInstance(obj_type.__dict__, types.MappingProxyType)
+        # tp_mro
+        self.assertEqual(obj_type.__mro__, (obj_type, tuple, object))
+        # tp_name
+        self.assertIsInstance(type.__name__, str)
+        # tp_subclasses
+        self.assertEqual(obj_type.__subclasses__(), [])
+
+    def test_sys_attrs(self):
+        for attr_name in (
+            'flags',          # FlagsType
+            'float_info',     # FloatInfoType
+            'hash_info',      # Hash_InfoType
+            'int_info',       # Int_InfoType
+            'thread_info',    # ThreadInfoType
+            'version_info',   # VersionInfoType
+        ):
+            with self.subTest(attr=attr_name):
+                attr = getattr(sys, attr_name)
+                self.check_structseq(type(attr))
+
+    def test_sys_funcs(self):
+        func_names = ['get_asyncgen_hooks']  # AsyncGenHooksType
+        if hasattr(sys, 'getwindowsversion'):
+            func_names.append('getwindowsversion')  # WindowsVersionType
+        for func_name in func_names:
+            with self.subTest(func=func_name):
+                func = getattr(sys, func_name)
+                obj = func()
+                self.check_structseq(type(obj))
+
+
+try:
+    unittest.main()
+except SystemExit as exc:
+    if exc.args[0] != 0:
+        raise
+print("Tests passed")