Charles Parham

Added documentation to the `Sign` enum fields to clarify meaning and intended usage. Resolves https://github.com/rust-num/num-bigint/issues/334.

to_bytes_le() returns [0] for some values

2

I ran across this behavior in my randomized tests: [Playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=0ec7f9e5e24b736ac2d7cb5e1b3d584d) ```rust use num_bigint::*; // 0.4.6 fn main() { let exp_bytes = [37, 134, 4, 249, 45, 233, 54, 83, 189,...