gh-81057: Add PyInterpreterState.static_objects (gh-99397)

As we consolidate global variables, we find some objects that are almost suitable to add to _PyRuntimeState.global_objects, but have some small/sneaky bit of per-interpreter state (e.g. a weakref list). We're adding PyInterpreterState.static_objects so we can move such objects there. (We'll removed the _not_used field once we've added others.)

https://github.com/python/cpython/issues/81057

Include/internal/pycore_global_objects.h

@@ -49,6 +49,24 @@ struct _Py_global_objects {
     PyObject *interned;
 };
 
+#define _Py_INTERP_CACHED_OBJECT(interp, NAME) \
+    (interp)->cached_objects.NAME
+
+struct _Py_interp_cached_objects {
+    int _not_set;
+};
+
+#define _Py_INTERP_STATIC_OBJECT(interp, NAME) \
+    (interp)->static_objects.NAME
+#define _Py_INTERP_SINGLETON(interp, NAME) \
+    _Py_INTERP_STATIC_OBJECT(interp, singletons.NAME)
+
+struct _Py_interp_static_objects {
+    struct {
+        int _not_used;
+    } singletons;
+};
+
 
 #ifdef __cplusplus
 }