* Don't allow \r in header names
From RFC 9112:
A sender MUST NOT generate a bare CR (a CR character not immediately
followed by LF) within any protocol elements other than the content.
A recipient of such a bare CR MUST consider that element to be invalid
or replace each bare CR with SP before processing the element or forwarding
the message.
net/http seems to completely error on this, so let's do the same.
Fixes https://github.com/valyala/fasthttp/issues/1785
* Validate the full header field