Include stylesheets downstream, including layouts in ChatMessage

[ahuang11]

Before (no message background, even though css class is set.):

After:

"""
Demonstrates how to use the `ChatInterface` to create a chatbot using
OpenAI's with async/await.
"""

import panel as pn
from openai import AsyncOpenAI

pn.extension()


async def callback(contents: str, user: str, instance: pn.chat.ChatInterface):
    response = await aclient.chat.completions.create(
        model="gpt-3.5-turbo",
        messages=[{"role": "user", "content": contents}],
        stream=True,
    )
    message = None
    parts = ""
    indicator = pn.indicators.Dial(name="Length")
    async for chunk in response:
        part = chunk.choices[0].delta.content
        if part:
            parts += part
            indicator.value = len(parts)
            layout = pn.Row(
                pn.pane.Markdown(parts, css_classes=["message"]),
                indicator,
            )
            yield layout


aclient = AsyncOpenAI()
chat_interface = pn.chat.ChatInterface(callback=callback, callback_user="ChatGPT")
chat_interface.send(
    "Send a message to get a reply from ChatGPT!", user="System", respond=False
)
chat_interface.servable()

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.66%. Comparing base (4581b4a) to head (8c7db6b).

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #6405       +/-   ##
===========================================
- Coverage   82.03%   71.66%   -10.38%     
===========================================
  Files         305      305               
  Lines       45730    45738        +8     
===========================================
- Hits        37515    32776     -4739     
- Misses       8215    12962     +4747     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	71.66% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[philippjfr]

I'm always a little wary for applying stylesheets inplace on objects the user created but I guess it's okay here.