Rust port of http-cache-semantics

As part of our current push on the `dstopic` side of things, @yoshuawuyts and I are working on [a caching http client](https://discourse.entropic.dev/t/writing-an-http-client-for-dstopic/204) that can cache its downloaded data down to [`cacache`](https://crates.io/crates/cacache).

But there's a piece missing! [`make-fetch-happen`](https://github.com/zkat/make-fetch-happen) was fortunate enough to be able to use an excellent package called [`http-cache-semantics`](https://github.com/kornelski/http-cache-semantics) which is a fairly complete implementation of http caching logic.

Your mission, should you choose to accept it, is to port `http-cache-semantics` over to Rust!

Now, I've already spoken with @kornelski about it, and they are sadly unable to pick up another project right now, but they were willing to share that [they had already started working on a port](https://gitlab.com/kornelski/http-cache-semantics-rs/blob/master/src/lib.rs), so this would be a great place to start, I think, for anyone willing to pick this up?

Are you interested in doing this? Can you do it in the fairly near future (since this is currently a blocker)? Reply below and let me know! We'd love your help! I'm totally willing to collaborate on this, as well. This is a **fantastic** way to learn Rust, if you're coming from the JS ecosystem, too.

([original thread](https://discourse.entropic.dev/t/looking-for-help-rust-port-of-http-cache-semantics/258?u=zkat))