feat(config): add Meta-Llama-3.1-8B-Instruct for MMLU benchmark

[6taco]

Add Llama-3.1-8B-Instruct configuration specifically for MMLU benchmark.

First-time contributor @6taco (CS undergraduate student seeking internship 2026). Thank you so much for reviewing!

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

Please describe the motivation of this PR and the goal you want to achieve through this PR.

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the backward compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here and update the documentation.

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

[6taco]

@Ying1123 @luyao25 老师好！我是大三在读学生，这是我第一次开源贡献，为 MMLU 新增了 Meta-Llama-3.1-8B-Instruct 配置，已在本地简单跑通，麻烦老师 review 合并一下，谢谢老师！🙏