add gpt-5.4-nano and mini#419

Ken Jiang (knjiang) merged 2 commits intomainbraintrustdata/braintrust-proxy:mainfrom

03-17-add_gpt-5.4-nano_and_minibraintrustdata/braintrust-proxy:03-17-add_gpt-5.4-nano_and_miniCopy head branch name to clipboard