feat: add sources

[stringhandler]

The sources here are manually generated.

I originally generated these using Haskell, as seen in my original repo, however that is controversial, so I've just included the sources for now.

The code can be tested by cloning this into a local folder, and then using a program like:

use std::assert::assert_eq8;

fn main() {

    let a: u8 = 1;
    let b: u8 = 2;

    assert_eq8(a, b);
}

Compile with simc program.simf --dep std=<path_to_local_folder>

e.g. simc program.simf --dep std=~/projects/simplicityhl-std/src

[stringhandler]

In hindsight I think we should split out methods for types that are Liquid/elements specific, for example into a separate module, possibly named std-elements.

For example, eq_asset1() would possibly not compile on Bitcoin.

[stringhandler]

Converting to draft as I believe @aritkulova will be working on this with simplex testing