feat: add thinking steps support as chunks to chat stream with plan and task blocks

[zimeg]

Summary

This PR adds support for thinking steps using chunks with chat stream or as blocks for other messages. This includes:

• The task_update chunk in feat: accept chunks as arguments to chat.{start,append,stop}Stream methods #1806 and feat: support and flush chunks in the chat stream helper #1809
• The markdown_text chunk in feat: accept chunks as arguments to chat.{start,append,stop}Stream methods #1806 and feat: support and flush chunks in the chat stream helper #1809
• The plan_update chunk in feat: add plan_update chunk for chat streaming #1821
• The task block in feat: add task_card and plan blocks #1819
• The plan block in feat: add task_card and plan blocks #1819

Testing

👾 Check out this sample: slack-samples/bolt-python-assistant-template#43

from slack_sdk.models.messages.chunk import TaskUpdateChunk

streamer = client.chat_stream(
    channel="C0123456789",
    recipient_team_id="T0123456789",
    recipient_user_id="U0123456789",
    thread_ts="1234567890.123456",
    task_display_mode="timeline",
)

streamer.append(
    chunks=[
        TaskUpdateChunk(
            id="task-1",
            title="Processing...",
            status="in_progress",
        ),
    ],
)

streamer.stop(
    chunks=[
        TaskUpdateChunk(
            id="task-1",
            title="Done!",
            status="complete",
        ),
    ],
)

from slack_sdk.models.blocks import (
    RichTextBlock,
    RichTextElementParts,
    RichTextSectionElement,
    TaskCardBlock,
    UrlSourceElement,
)
...
client.chat_postMessage(
    channel="C0123456789",
    blocks=[
        TaskCardBlock(
            task_id="000",
            title="Living life well...",
            status="error",
            details=RichTextBlock(
                elements=[
                    RichTextSectionElement(
                        elements=[
                            RichTextElementParts.Text(text="Dreamt of touching grass"),
                        ],
                    ),
                ],
            ),
            sources=[
                UrlSourceElement(
                    text="An online encyclopedia",
                    url="https://wikipedia.org",
                ),
            ],
            output=RichTextBlock(
                elements=[
                    RichTextSectionElement(
                        elements=[
                            RichTextElementParts.Text(text="Good things once happened"),
                        ],
                    ),
                ],
            ),
        ),
    ],
)

Category

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.models (UI component builders)
• /docs (Documents)
• 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

❌ Patch coverage is 89.87342% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.96%. Comparing base (c697f35) to head (953407f).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
slack_sdk/models/messages/chunk.py	73.33%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1824      +/-   ##
==========================================
+ Coverage   83.91%   83.96%   +0.05%     
==========================================
  Files         115      116       +1     
  Lines       13080    13221     +141     
==========================================
+ Hits        10976    11101     +125     
- Misses       2104     2120      +16     

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[srtaalej]

great PR description! thanks for these changes 🦋 💟