> See branch https://github.com/kumaraditya303/cpython/commits/fix-code

Oh nice, I like this new _Py_Deepfreeze_Fini() function :-) I suggest to create a function specific to only clear immortal code objects. In my experience, it's important to control exactly when objects are cleared at Python exit: Py_Finalize() is complex and fragile. See my notes:
https://pythondev.readthedocs.io/finalization.html

Be careful, Python must remain usable after Py_Finalize(): it's legit to call Py_Initialize() again and execute new Python code. Example executing the same code 4 times, each time Py_Initialize() and Py_Finalize() are called:

./Programs/_testembed test_repeated_init_exec 'print("Hello")'

My _PyStaticMethod_Dealloc() implementation uses Py_CLEAR() rather than Py_XDECREF() to set structure members to NULL.

Moreover, there are more things than just co_quickened which should be cleared. I suggest to add a new function to clear an "immortal" code object. For example, I also suggest to call PyObject_ClearWeakRefs(). I guess that co_extra should also be cleared.