Fix num_logprobs parameter description in sampler.py

[zhuohan123]

Purpose

Corrected the description of num_logprobs parameter. It should be maximum number of logprobs across the requests instead of minimum.

Test Plan

Test Result

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request corrects the description of the num_logprobs parameter in the gather_logprobs function's docstring. The change from 'minimum' to 'maximum' is accurate, as this parameter represents the highest number of logprobs requested across all sequences in a batch, and torch.topk is used to retrieve that number of top logprobs. The change improves the clarity and correctness of the documentation. The change is correct and I have no further suggestions.