Allow interrupting sync calls midway for ChatInterface

[ahuang11]

Makes it so that sync tasks are submitted to a separate thread so it's cancellable.

Screen.Recording.2023-12-04.at.10.58.51.PM.mov

import panel as pn
from openai import OpenAI

pn.extension()


def callback(contents: str, user: str, instance: pn.chat.ChatInterface):
    response = client.chat.completions.create(
        model="gpt-3.5-turbo",
        messages=[{"role": "user", "content": contents}],
        stream=True,
    )
    message = None
    for chunk in response:
        part = chunk.choices[0].delta.content
        if part is not None:
            message = instance.stream(part, user="OpenAI", message=message)


client = OpenAI()
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.stream("Hello")
chat_interface.show()

[codecov]

Codecov Report

Attention: 38 lines in your changes are missing coverage. Please review.

Comparison is base (1fb5aa8) 84.41% compared to head (30e9891) 40.77%.

❗ Current head 30e9891 differs from pull request most recent head e67f52e. Consider uploading reports for the commit e67f52e to get more accurate results

Files	Patch %	Lines
panel/chat/feed.py	16.66%	30 Missing ⚠️
panel/chat/interface.py	20.00%	4 Missing ⚠️
panel/tests/chat/test_feed.py	0.00%	3 Missing ⚠️
panel/tests/chat/test_interface.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##           add_interrupt_async    #5990       +/-   ##
========================================================
- Coverage                84.41%   40.77%   -43.65%     
========================================================
  Files                      291      291               
  Lines                    43544    43544               
========================================================
- Hits                     36757    17753    -19004     
- Misses                    6787    25791    +19004     

Flag	Coverage Δ
ui-tests	40.77% <17.39%> (-0.01%)	⬇️
unitexamples-tests	?

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[hoxbro]

Was this PR ready to be merged? Failing tests seem very relevant.

Edit: I can see it was not merged into main. Sorry for the noise.