Add multithreading test to model compare binary (#80958)
This diff adds a option (`--nthreads`) which will launch the specified number of threads to load the models execute the correctness check on them.
Differential Revision: [D37465661](https://our.internmc.facebook.com/intern/diff/D37465661/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80958
Approved by: https://github.com/manuelcandales
