[LesterEvSe]

Previously, this functionality was deleted in #323 along with the old mod keyword support, but the lexer and parser still support this. So now we reintroduce const.

The main reason we need it is to avoid using functions where a const would be enough. A simple example is the sha256_paddings.simf file in the price-oracle repo.

So now we can do something like this:

mod config {
    pub const FEE: u32 = 1_000;
}

use crate::config::FEE;

const MAX: u32 = 10_000;

fn main() {
    assert!(jet::lt_32(FEE, MAX));
}

NOTE: It's better to review this after #451 is merged.

Checklist

• New or changed language features are used in fixtures/kitchen_sink.simf (see its header).