Add streaming support

[transitive-bullshit]

Opening an issue to track this feature, since it seems to keep coming up, and I'm expecting to make use of it soon for a project.

See also:

• https://www.beskar.co/blog/streaming-openai-completions-vercel-edge
• https://www.npmjs.com/package/@beskar-labs/parse-json-sse
• https://github.com/transitive-bullshit/chatgpt-api/blob/main/src/fetch-sse.ts

[rileytomasek]

Streaming would be great. Do you know if it's possible with Ky?

[dglazkov]

@transitive-bullshit if you'd like, try the patch I submitted for review.