feat(parser): move definitions to their own modules

crates/aiken-lang/src/parser/utils.rs

@@ -0,0 +1,7 @@
+use chumsky::prelude::*;
+
+use super::{error::ParseError, token::Token};
+
+pub fn public() -> impl Parser<Token, (), Error = ParseError> {
+    just(Token::Pub).ignored()
+}