[8/n] [torch/elastic] Add unit tests for _RendezvousState (#56536)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56536
This PR adds unit tests to ensure that the encoded byte length of `_RendezvousState` stays under a certain limit.
ghstack-source-id: 127626622
Test Plan: Run the newly-introduced unit tests.
Reviewed By: tierex
Differential Revision: D27890704
fbshipit-source-id: 24905c8bc9d985d5ee90d370f28739eb137ce0f0
