Fix prompt len in parallel sampling

[yichuan520030910320]

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Motivation

Fix prompt len in parallel sampling

Modification

openai Adapter and resolve one fixme in test openai API

Checklist

1. Ensure pre-commit pre-commit run --all-files or other linting tools are used to fix potential lint issues.
2. Confirm that modifications are covered by complete unit tests. If not, please add more unit tests for correctness.
3. Modify documentation as needed, such as docstrings or example tutorials.