Add fc to HF export

[dakinggg]

The HF export was missing the fc.py file and the associated register, so would result in an error when trying to load the HF exported model. This PR both fixes the issue, and adds a unit test that would've caught it, which requires clearing the registry for the unit test to simulate a fresh environment.

The move of MultiTokenEOSCriteria is just because Composer dev has removed that class, and it is now in foundry.