Expose /fast mode usage in session logs

What variant of Codex are you using?

CLI

What feature would you like to see?

I use https://github.com/ryoppippi/ccusage to track my billing. It would be nice to include the service_tier somewhere there, as it influences the price (a lot). Currently only token usages are there which isn't sufficient to compute the cost of a session.

Additional information

_No response_