fix: lenient chunk extension parsing leading to request smuggling issues

[JeppW]

fasthttp allows newlines (\n) between the chunk size and the CRLF (i.e. in the chunk extension). This can cause request smuggling issues with some reverse proxies. This PR prevents this potential vulnerability by disallowing newlines in the chunk extension.

I've also corrected two unescaped carriage returns in error messages which messed with the output formatting.

[erikdubbelboer]

Can you fix the lint issue?

http.go:2518:13: fmt.Errorf can be replaced with errors.New (perfsprint)
  					error: fmt.Errorf("invalid character '\\n' after chunk size")

[JeppW]

Should be okay now, can you rerun the workflows?

[erikdubbelboer]

Thanks!

[JLLeitschuh]

This looks like it fixed a legitimate security vulnerability. Shouldn't a CVE be assigned? Would the fasthttp be willing to facilitate this? @erikdubbelboer

Would you be willing to open a GitHub security advisory here? https://github.com/valyala/fasthttp/security

Issue tracking for CVE assignment: JLLeitschuh/unCVEed#1