Provide an allocation free interface

[ducdetronquito]

As proposed by @kristoff-it;

I would be interested in seeing also an interface that doesn't require an allocator.
You need to do a bit of gymnastics with tuples to get there, but it should be doable. The trick is to have the builder ask for all parameters upfront, so that it can provide a return type appropriately computed.

Cf: https://old.reddit.com/r/Zig/comments/ixwl3w/http_core_types_for_zig/g69jc67/