stream mode supports output schema

[Undertone0809]

🚀 Feature Request

Now pne cannot use stream + output_schema. For example:

import pne
from pydantic import BaseModel

class LLMResponse(BaseModel):
    content: str = Field(..., description="LLM response content")

response = pne.chat(model="gpt-4o", stream=True, output_schema=LLMResponse)

It will get error if you run this example.

This feature should build after #625.