[Feature Request] Support Streaming messages

[yongzhang]

Description

(Optional) Slack's documentation

Ref: https://docs.slack.dev/changelog/2025/10/7/chat-streaming/

Thanks.

[dnck]

@nlopes I would nominate myself for work on this feature if you don't already have it in your current scope of work. Happy to lend a hand in this awesome project.

[nlopes]

Happy for you to do so. I intend to work on it over the weekend so if you get there first go for it. If not, I'll let you know here before I start work on it.