Server-Sent Event support in both modes

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You should probably consider this a draft to clean up before merging, as it comes straight from our new dev and this is pretty much his first bit of serious OCaml. I'm attaching the test files to this message, although those are of limited value since they were from our monorepo. They might inspire you though. 😉

ezcurl_sse_tests.tar.gz

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I'd prefer following the standard and treating them, indeed, as comments :-)

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I'd prefer following the standard and treating them, indeed, as comments :-)

I thought I saw some use them in the wild, but I just double-checked Anthropic and it doesn't use them. Not sure where I saw them then. I still see it as risky to delete them outright but I won't oppose it since we're focused on Anthropic.

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I haven't touched this PR yet, so if things got added or removed something else is modifying things. (In fact I've been sick all this week, so I definitely didn't touch this.)