open_ai: Fix issues with OpenAI compatible APIs (#32982)

Ran into this while adding support for Vercel v0s models:
- The timestamp seems to be returned in Milliseconds instead of seconds
so it breaks the bounds of `created: u32`. We did not use this field
anywhere so just decided to remove it
- Sometimes the `choices` field can be empty when the last chunk comes
in because it only contains `usage`

Release Notes:

- N/A
c34b24b5fbBennet Bo Fenner committed on 6/18/2025, 9:51:51 PM· committed by GitHubparent05f944b
2 files changedLine totals unavailable