Code of simple_chat is over-complicated.

[polina-c]

Code of simple_chat should be compact, easy to read and deal with a small number of clearly defined concepts of GenUI SDK.

In addition, we need to setup some continuous validation for this simplicity, because we already worked to simplify simple_chat before.

[polina-c]

Adding details.

As explained in the previous issue, simple_chat should demonstrate that it is easy to convert a simple AI-text-chat application to AI-UI-chat application.

This means GenUI related code of the app should be compact, self-explaining and well-readable, that currently is not the case.

Complicated pieces:

• AiClientTransport
• ChatSession

In addition to removing complexity, we want the diff between text and UI chat to be visible.
It may be that we may want to keep two code bases of simple_chat - text only and with UI.
Or, we may want to highlight GenUI related code with comments, so that they are clearly visible.