feat: add authorship arguments to assistant threads and chat stream

[zimeg]

Summary

This pull request adds authorship arguments (icon_emoji, icon_url, username) to the assistant.threads.setStatus and chat.startStream Web API methods.

Mirrors slackapi/node-slack-sdk#2455 for the Python SDK.

Testing

Try the following snippet against an assistant thread:

import time

client.assistant_threads_setStatus(
    channel_id="C018QLSQ38A",
    thread_ts="1765934795.222209",
    status="dancing...",
    username="Charlie Brown",
    icon_emoji="maple_leaf",
)

time.sleep(4)

response = client.chat_startStream(
    channel="C018QLSQ38A",
    thread_ts="1765934795.222209",
    recipient_team_id="T07L2FPUY",
    recipient_user_id="U0187GKV2US",
    username="Charlie Brown",
    icon_emoji="maple_leaf",
)

time.sleep(2)

client.chat_appendStream(
    channel="C018QLSQ38A",
    ts=response["ts"],
    markdown_text="Dancing with snoopy dog.",
)

time.sleep(2)

client.chat_stopStream(
    channel="C018QLSQ38A",
    ts=response["ts"],
)

streamer = app.client.chat_stream(
    channel="C07U19RTY90",
    thread_ts="1777925328.173729",
    recipient_user_id="U06MCF88LQY",
    recipient_team_id="T06M2FAFCF3",
    username="Charlie Brown",
    icon_emoji="maple_leaf",
    buffer_size=0,
)
streamer.append(markdown_text="Dancing with snoopy dog!")
time.sleep(2)
streamer.append(markdown_text=" Fun!")
streamer.stop()

Category

• slack_sdk.web.WebClient (sync/async) (Web API client)
• tests/integration_tests (Automated tests for this library)

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.00%. Comparing base (726538c) to head (c623822).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1862      +/-   ##
==========================================
- Coverage   84.00%   84.00%   -0.01%     
==========================================
  Files         117      117              
  Lines       13257    13257              
==========================================
- Hits        11137    11136       -1     
- Misses       2120     2121       +1     

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[srtaalej]

Looks great and working well for me ⭐ ⭐ ⭐

[zimeg]

@srtaalej Thanks so much for reviewing! I landed c623822 after reading the linked issue again to find that the included chat_stream helper requires these same arguments be defined for editor hints 🔍 ✨

The description has updated test steps if that's curious but I will plan to merge this soon otherwise 🚢