[sglang] Adapting the use of _launch_subprocesses to the latest SGLang branch

[xiazhahe]

What does this PR do?

The latest main branch of SGLang has wrapped the _launch_subprocesses function inside the Engine class. Adapt and add the use of _launch_subprocesses to the latest SGLang branch.

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[gemini-code-assist]

Code Review

This pull request introduces compatibility for newer versions of SGLang (post-0.5.9) by implementing a feature check for the Engine class. It updates the server launch logic to use Engine._launch_subprocesses when available, while maintaining backward compatibility for older versions through a fallback mechanism. I have no feedback to provide.

[wucong25]

如果在这里判断SGLangr version newer than 0.5.9，然后再导包的话 感觉代码形式上稍微解耦一点