fix: improve SSE stream response handling and add fasthttp support (#888)

[zhouyusd]

Fix #888

[Copilot]

Pull request overview

Improves Server-Sent Events (SSE) streaming response handling by refactoring message sending and adding a fasthttp/Fiber-specific streaming implementation.

Changes:

• Refactors SSE message writing into a reusable internal send(...) helper that accepts writer/encoder/flusher/deadliner dependencies.
• Adds a fasthttp (*fasthttp.RequestCtx) streaming path using SetBodyStreamWriter to support Fiber/fasthttp response streaming.

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[wolveix]

Hey @zhouyusd! Thanks for taking the time to implement this. Unfortunately, we're strictly against importing excessive dependencies in the core Huma library unless they're absolutely necessary; with your implementation, all Huma users would have to import fasthttp. With this in mind, I created #1059 which introduces a small internal streaming hook. I referenced you directly in that PR.

Thanks again!