The async lib doesn't supports timeout, meaning not usable in production or any serious workload.
I can see where you get that idea from, indeed the httpclient module doesn't have timeout flags for it's async recieve. But the asyncdispatch has a withTimeout procedure that should happily take the Future that you get from an async recieve and give you a timeout for it.
https://nim-lang.github.io/Nim/httpclient
https://github.com/nim-lang/Nim/commit/783087fd