Allow stopping respond callbacks midway

[ahuang11]

Closes #5943

Upon sending a message, if the callback is async, the Send button gets hidden and the Stop button appears. Clicking it will cancel the callback midway.

Screen.Recording.2023-11-30.at.3.58.11.PM.mov

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()

Also, I think I made it more performant for sync too.

[codecov]

Codecov Report

Attention: 13 lines in your changes are missing coverage. Please review.

Comparison is base (7e3d985) 84.67% compared to head (ebba0ef) 84.67%.

Files	Patch %	Lines
panel/tests/util.py	71.42%	8 Missing ⚠️
panel/tests/chat/test_interface.py	95.00%	2 Missing ⚠️
panel/chat/feed.py	98.03%	1 Missing ⚠️
panel/chat/interface.py	95.00%	1 Missing ⚠️
panel/tests/chat/test_feed.py	98.03%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5962      +/-   ##
==========================================
- Coverage   84.67%   84.67%   -0.01%     
==========================================
  Files         291      291              
  Lines       43586    43722     +136     
==========================================
+ Hits        36907    37020     +113     
- Misses       6679     6702      +23     

Flag	Coverage Δ
ui-tests	40.67% <16.93%> (-0.08%)	⬇️
unitexamples-tests	72.84% <93.15%> (+0.03%)	⬆️

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[philippjfr]

Still seeing some errors in the tests.

[ahuang11]

Okay fixed the issue: generators are "finished" prematurely from the POV of a future, so I had to introduce a _callback_state param that track whether it's a generator and stop it manually.