PyAPI: support Python 3.13

- `_PySet_NextEntry` has been removed, use generic iterator access
  which will has some additional overhead as it needs to create
  an iterator to access the values.

- Add v3.13 compatibility defines to account for renaming:
  _PyObject_LookupAttr -> PyObject_GetOptionalAttr
  _PyLong_AsInt -> PyLong_AsInt

- Unfortunately use of Python's internal API needs to be used to
  inspect op-codes in `bpy_driver.cc`.

Testing GLTF/FBX IO there isn't any significant performance impact
from these changes.

Resolves #123871.

source/blender/python/generic/python_compat.hh

@@ -9,9 +9,17 @@
 
 #pragma once
 
+/* Removes `intialized` member from Python 3.13+. */
+#if PY_VERSION_HEX >= 0x030d0000
+#  define PY_ARG_PARSER_HEAD_COMPAT()
+#elif PY_VERSION_HEX >= 0x030c0000
 /* Add `intialized` member for Python 3.12+. */
-#if PY_VERSION_HEX >= 0x030c0000
 #  define PY_ARG_PARSER_HEAD_COMPAT() 0,
 #else
 #  define PY_ARG_PARSER_HEAD_COMPAT()
 #endif
+
+/* Python 3.13 made some changes, use the "new" names. */
+#if PY_VERSION_HEX < 0x030d0000
+#  define PyObject_GetOptionalAttr _PyObject_LookupAttr
+#endif