feat: use singular bytes for the jumpmap

[onbjerg]

Switches from usize to u8 for easier encoding, and adds some methods to build a jump map from a u8 slice

[rakita]

Is it better to have u8 or u64?

[onbjerg]

There is probably not much of a difference performance wise, but encoding/decoding (which almost always is represented as some operation from X -> &[u8] and &[u8] -> X) will be a lot more annoying with u64, since you would need to turn slices of u64 to slices of u8, and slices of u8 to slices of u64.

[rakita]

Yeah, will check in the future if there is some degradation (I assume there is none), and having u8 is easier to handle.