有提供stream模式吗，类似打字机的效果。

**What problem does this feature solve? **
我需要对接大语言模型，输出不是一次性的。

**Describe the solution you'd like **
暂无，能否支持这个功能。

**What does the proposed API look like? **
提供一个支持stream模式的api

No file, test, or implementation entry point is named. Start by reading the existing ChatUI API and React message-rendering flow, then determine how incremental model output should be represented and exposed. The issue is done when a defined streaming API supports the requested typewriter-like display and its behavior is verified.

Written by the indexing model from the issue text.