Bugfixing completion stats break with new reasoning tokens release

[lucapericlp]

Fixes #1556

Note for reviewers, I've removed the template given that it was strictly related to evals.

I've not added any test coverage given the lack of it in this repo.

[sjadler2004]

Thank you for trying to address this! I still get the same error unfortunately, e.g., when running oaieval gpt-4-32k 2d_movement.

I'm going to put the usage-token stats inside of a try: for now, so that this bug does not disrupt the evals completing properly.

[sjadler2004]

#1560