HTTP spec. compliance testing

A basic HTTP RFC9112 spec. compliance test has been added and minor changes have been made to pass all tests immediately:

This basic test catches no issues in Node.js, but it catches 2 issues in Deno (reported). The test can be found here:

https://github.com/uNetworkingAB/h1spec

In contrast, running the test on completely broken servers like mrhttp you get an obvious indication of so: