[TPU][Bugfix] fix moe layer

[yaochengji]

Purpose

To fix the issue on TPU introduced by #20775, where several new arguments in moe layer are introduced, but forward_tpu doesn't handle them.

• fix moe layer
• add a TPU MoE test

Test Plan

pytest -s -v tests/v1/tpu/test_basic.py

Test Result

Passed

(Optional) Documentation Update

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.

💬 Join our developer Slack at https://slack.vllm.ai to discuss your PR in #pr-reviews, coordinate on features in #feat- channels, or join special interest groups in #sig- channels.

Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can either: Add ready label to the PR or enable auto-merge.

🚀

[gemini-code-assist]

Code Review

This pull request fixes a bug in the MoE layer for TPU by allowing forward_tpu to accept new arguments. It also adds a new MoE model to the TPU test suite. The fix is correct, but I've suggested an improvement to make the function signature more explicit and robust against future changes, which will improve maintainability.