Deduplicate Python object serialization (#57858)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57858
Just a small deduplication, which move complexity our of the way, and ensures consistent error checking.
ghstack-source-id: 129567056
Test Plan: CI
Reviewed By: mrshenli
Differential Revision: D28286174
fbshipit-source-id: 6eab8d3f30405d49c51f8b9220453df8773ff410
