refactor: update argument parsing for multi-machine launches.

[XuZhang99]

Description

This Refactor is for xllm serve(python-interface launch method).

• Renamed --node_rank to --machine_rank for clarity.
• Enhanced help descriptions for --machine_rank and --nnodes.
• Added validation for --machine_rank and device count detection.
• Introduced _reject_managed_flags to prevent manual setting of --node_rank.
• Updated launch target resolution to accommodate multi-machine configurations.

Related Issues

Change Type

• Bug fix
• New feature
• Performance improvement
• Refactor
• Documentation
• Test
• Build or CI

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Reviewer Notes