v3.40.0.dev0

<!-- Release notes generated using configuration in .github/release.yml at feat-ai-apps-thinking-steps -->

What's Changed

🚀 Enhancements

• feat: accept chunks as arguments to chat.{start,append,stop}Stream methods by @zimeg in https://github.com/slackapi/python-slack-sdk/pull/1806
• feat: support and flush chunks in the chat stream helper by @zimeg in https://github.com/slackapi/python-slack-sdk/pull/1809
• feat: add task_card and plan blocks by @zimeg in https://github.com/slackapi/python-slack-sdk/pull/1819
• feat: add task_display_mode option to the start of chat streams by @zimeg in https://github.com/slackapi/python-slack-sdk/pull/1820
• feat: add plan_update chunk for chat streaming by @zimeg in https://github.com/slackapi/python-slack-sdk/pull/1821

🐛 Bug Fixes

• fix: move away from datetime.utcfromtimestamp for the state and installation stores by @WilliamBergamin in https://github.com/slackapi/python-slack-sdk/pull/1798
• fix: broken link to CI from readme by @WilliamBergamin in https://github.com/slackapi/python-slack-sdk/pull/1805

📦 Other changes

• chore(deps): bump actions/checkout from 5.0.0 to 6.0.0 by @dependabot[bot] in https://github.com/slackapi/python-slack-sdk/pull/1799
• chore(deps): bump actions/setup-python from 6.0.0 to 6.1.0 by @dependabot[bot] in https://github.com/slackapi/python-slack-sdk/pull/1800
• chore(deps): bump docutils from 0.22.2 to 0.22.3 by @dependabot[bot] in https://github.com/slackapi/python-slack-sdk/pull/1802
• chore(deps): update mypy requirement from <=1.18.2 to <=1.19.0 by @dependabot[bot] in https://github.com/slackapi/python-slack-sdk/pull/1801
• fix: improve CI and helper scripts by @WilliamBergamin in https://github.com/slackapi/python-slack-sdk/pull/1803

Full Changelog: https://github.com/slackapi/python-slack-sdk/compare/v3.39.0...v3.40.0.dev0