* Add _PyAtExit_Call() function and remove pyexitfunc and
pyexitmodule members of PyInterpreterState. The function
logs atexit callback errors using _PyErr_WriteUnraisableMsg().
* Add _PyAtExit_Init() and _PyAtExit_Fini() functions.
* Remove traverse, clear and free functions of the atexit module.
Co-authored-by: Dong-hee Na <donghee.na@python.org>