Investigate the `http-desync-guardian` crate

As was pointed out [on Reddit](https://www.reddit.com/r/rust/comments/kfbrce/announce_asynch1_230_tide_requestsmuggling/gg82svm/?utm_source=reddit&utm_medium=web2x&context=3) during our `2.3.0` security release, prior art exists on guarding against desync (request smuggling) attacks. [http-desync-guardian](https://github.com/aws/http-desync-guardian) is a library which may be able to assist us in catching desync attacks. At the least it's worth looking at, and if we thing the techniques it uses are worthwhile, then integrate either directly, or port to a shape that works for us.

Start by reviewing the linked http-desync-guardian crate and the current async-h1 HTTP/1.1 request parsing behavior. Determine whether its desync-defense techniques fit this project and whether integration or a port is appropriate; done requires a documented direction and, if adopted, an agreed implementation scope.

Written by the indexing model from the issue text.