[Feature]: `kv_transfer_params` not returned for multiple subrequests

[jianzs]

🚀 The feature, motivation and pitch

Currently, when handling HTTP requests with multiple subrequests, the response only includes kv_transfer_params for one subrequest, making it impossible to access KV transfer information for other subrequests.

Related PR: #17751
Reference code:

vllm/vllm/entrypoints/openai/serving_completion.py

Lines 514 to 520 in e384f2f

	return CompletionResponse(
	id=request_id,
	created=created_time,
	model=model_name,
	choices=choices,
	usage=usage,
	kv_transfer_params=final_res_batch[0].kv_transfer_params)

Alternatives

No response

Additional context

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