[worker, sglang] fix: Rename the file sglang_router.py to avoid circular imports

[Shiguang-Guo]

What does this PR do?

Rename the file sglang_router.py to avoid circular imports, which prevent the correct sglang_router from being recognized.

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[gemini-code-assist]

Code Review

This pull request correctly resolves a module shadowing issue by renaming sglang_router.py to inner_sglang_router.py. The change is sound. I've added a couple of suggestions for the renamed file to improve type hint correctness and startup robustness.