[WIP] Add stream output support for PyTorch backend on Ascend

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

让pytorch后端的ascend上也可以用在线server启动后，用下面的命令stream输出。
curl -N -X POST http://localhost:40001/v1/chat/completions
-H "Content-Type: application/json"
-d '{
"model": "qwen3-0.6b",
"messages": [{"role": "user", "content": "介绍一下你自己"}],
"stream": true
}'

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