feat: add function to parse HTTP header parameters

[nickajacks1]

The implementation is based on RFC-9110 5.6.6.

https://www.rfc-editor.org/rfc/rfc9110#name-parameters

The primary use case for parsing header parameters is for content negotiation, including multipart type boundaries.

The functor passed to VisitHeaderParams has a bool return value to allow the user to stop processing parameters early.
Examples of this being useful are to find a specific parameter, stop parsing after the q value, or to put a hard limit on the number of parameters a client can include.

I had originally written this for a different project using fasthttp, but I figured it was generic enough that it may warrant being merged in for others to use as well. If not, no feelings will be hurt.

The implementation of validHeaderFieldByte is a little silly looking, but it's as fast as I could get it.
The Go standard library has its own implementation here, which is a bit slower: https://github.com/golang/go/blob/master/src/net/textproto/reader.go#L663
If the table solution is too arcane, we can copy the standard library instead.

Side note: VisitHeaderParams could also be used in MultipartFormBoundary to make fewer assumptions about how the client formatted their Content-Type header, but it would slow the function down quite a bit.
On my machine, it's 20 ns/op today vs 40 ns/op using VisitHeaderParams.

[erikdubbelboer]

It's very hard to see if VisitHeaderParams has any bugs that might cause panics for example. Can you add a FuzzVisitHeaderParams to fuzz it and see if it crashes?

[nickajacks1]

I see that existing fuzz tests use fuzzit, but given that the CI only builds on 1.18 and above and that there are no docs mentioning fuzzit, I just created a Fuzz test in header_test.go instead.

Ran a short 14 min fuzz:
fuzz: elapsed: 14m5s, execs: 27008124 (33905/sec), new interesting: 34 (total: 50)

[erikdubbelboer]

Yeah fuzzit used to fuzz fasthttp for free, I still need to rewrite the fuzz tests to the new Go fuzzers. Thanks for adding the fuzz test. Everything looks good, thanks!