[feat] support customized and separated hccl_buffer_size for process group initialization

[linfeng-yuan]

What this PR does / why we need it?

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.10.2
• vLLM main: vllm-project/vllm@9607d5e

[github-actions]

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[gemini-code-assist]

Code Review

This pull request aims to introduce support for customized hccl_buffer_size during process group initialization. While the intent is clear, the current implementation contains several critical errors, including missing imports, syntax errors, and incorrect function calls. These issues will prevent the code from running and must be addressed. I have provided specific feedback on each issue to help resolve them.