feat: add authorship arguments to say_stream

[zimeg]

Summary

This PR adds icon_emoji, icon_url, and username authorship arguments to SayStream, AsyncSayStream, SetStatus, and AsyncSetStatus helpers to match the new authorship support added in slack_sdk v3.42.0 🚀

• feat: add authorship arguments to assistant threads and chat stream python-slack-sdk#1862

Testing

@app.event("assistant_thread_started")
def handle_thread(say_stream, set_status):
    set_status(
        status="thinking...",
        icon_emoji=":maple_leaf:",
        username="Charlie Brown",
    )
    stream = say_stream(icon_emoji=":maple_leaf:", username="Charlie Brown")
    stream.append(markdown_text="Dancing with snoopy dog!")
    stream.stop()

Category

• slack_bolt.App and/or its core components
• slack_bolt.async_app.AsyncApp and/or its core components

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 ./scripts/install_all_and_run_tests.sh after making the changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.30%. Comparing base (3319330) to head (2e6e1f7).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1502   +/-   ##
=======================================
  Coverage   91.30%   91.30%           
=======================================
  Files         228      228           
  Lines        7271     7271           
=======================================
  Hits         6639     6639           
  Misses        632      632           

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[zimeg]

⚡ Similar changes might not be needed in Bolt JS with the subtracted arguments:

https://github.com/slackapi/bolt-js/blob/ba4deb6a8b39da43cef0452d7541bcfcc3f3527a/src/context/create-say-stream.ts#L5