[RPC profiling] Add tests to ensure RPC profiling works on single threaded (#44923)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44923
This ensures that RPC profiling works in single-threaded server
scenarios and that we won't make the assumption that we'll have multiple
threads when working on this code. For example, this assumption resulted in a
bug in the previous diff (which was fixed)
ghstack-source-id: 112868469
Test Plan: CI
Reviewed By: lw
Differential Revision: D23691304
fbshipit-source-id: b17d34ade823794cbe949b70a5ab35723d974203
