add repetition penalty

[Yunnglin]

see #443 (comment)

[Copilot]

Pull Request Overview

This PR adds support for a new repetition_penalty parameter through the arguments parser and ensures it is sent in the OpenAI API plugin, and updates the CLI tests to reflect expanded generation config options.

• Introduce repetition_penalty in the Arguments class and CLI parser
• Map repetition_penalty into the payload in the OpenAI API plugin
• Update CLI test to use a broader set of sampling parameters

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tests/cli/test_run.py	Expanded --generation-config string to include sampling options
evalscope/perf/plugin/api/openai_api.py	Added repetition_penalty field mapping in API payload
evalscope/perf/arguments.py	Added repetition_penalty argument and CLI parser option

Comments suppressed due to low confidence (2)

tests/cli/test_run.py:66

• The new repetition_penalty parameter is not included in this CLI test's generation-config string, so its behavior isn't covered. Consider adding repetition_penalty=<value> to ensure test coverage for this flag.

f'--generation-config do_sample=true,temperature=0.6,max_length=65535,max_new_tokens=65535,max_tokens=65535,n=1,top_p=0.95,top_k=20 ' \

evalscope/perf/plugin/api/openai_api.py:78

• [nitpick] Consider adding a brief comment or updating external documentation to explain how repetition_penalty influences model output, improving clarity for future maintainers.

if param.repetition_penalty is not None: