feat: add gpt-5.3-codex model support

[vincentkoc]

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WIP PR as API is not publicly released yet.

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Project	Deployment	Actions	Updated (UTC)
litellm	Ready	Preview, Comment	Feb 6, 2026 4:50am

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[zooneon]

hi @vincentkoc , The API is publicly now, so please open this PR.

• https://developers.openai.com/api/docs/models/gpt-5.3-codex

Thanks!

[vincentkoc]

Superseded by merged GPT-5.3 work on main (#22035 for gpt-5.3-codex and #22693 for gpt-5.3-chat-latest) plus follow-up ChatGPT OAuth alias coverage in #22734. Closing this stale draft to reduce duplication.