Minor bug fix: Make SkyRL's vllm engine compatible with higher versions of VLLM

[zhenga1]

OpenAIServingModels from VLLM has different signatures depending on version

[gemini-code-assist]

Code Review

This pull request addresses a compatibility issue with newer versions of the VLLM library by dynamically checking the signature of OpenAIServingModels before instantiation. This is a good approach to maintain compatibility across library versions. My review includes a suggestion to make this version check more robust by inspecting parameter names instead of the parameter count, and also includes some minor code cleanup.

[gemini-code-assist]

This is a good way to handle different versions of vllm. However, checking the number of parameters can be brittle if future versions add new optional parameters. A more robust approach would be to check for the existence of the model_config parameter in the signature. I've also cleaned up the commented-out code and removed the extra blank lines for better readability.

Suggested change

	from inspect import signature
	sig = signature(OpenAIServingModels)
	base_model_paths = [BaseModelPath(name=model_name, model_path=model_path)]
	models = OpenAIServingModels(engine, model_config, base_model_paths)
	if len(sig.parameters) == 4:
	# For OLD vllm (<0.11.2)
	models = OpenAIServingModels(engine, model_config, base_model_paths)
	else:
	# For NEW vllm (>= 0.11.2)
	models = OpenAIServingModels(engine, base_model_paths=base_model_paths)#model_config)
	from inspect import signature
	sig = signature(OpenAIServingModels)
	base_model_paths = [BaseModelPath(name=model_name, model_path=model_path)]
	if 'model_config' in sig.parameters:
	# For OLD vllm versions that have the 'model_config' parameter
	models = OpenAIServingModels(engine, model_config, base_model_paths)
	else:
	# For NEW vllm versions
	models = OpenAIServingModels(engine, base_model_paths=base_model_paths)