Add sglang sglang check env cpu fallback

[ghangz]

Summary

• Adds a focused sglang check env cpu fallback improvement for MetaX-MACA/sglang.
• The change targets MetaX MACA development and validation workflows, with emphasis on earlier diagnostics, reproducible logs, or safer benchmark tooling.
• Existing default behavior is kept compatible; the new logic is scoped to explicit checks, helper tools, or validation metadata.

Validation

• Verified on Gitee.AI MetaX GPU resources: sglang_SGLang image batch, 12/12 PASS; PyTorch-MACA batch also covered SGLang tooling.
• Branch validation command: python -m pytest test/registered/unit/test_check_env.py
• Pull request text is intentionally ASCII-only to avoid encoding issues on web forms and API clients.

Review notes

• Source branch: ghangz:mengz/sglang-check-env-cpu-fallback
• Target branch: MetaX-MACA/sglang:main
• Maintainers can modify this branch if follow-up adjustments are needed.

[gemini-code-assist]

Code Review

This pull request introduces a CPUEnv class to python/sglang/check_env.py to serve as a fallback environment checker when no supported accelerator backend is available. It also adds a corresponding unit test in test/registered/unit/test_check_env.py to verify its behavior. I have no feedback to provide as there are no review comments to evaluate.

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