Count labels in properties.

We'll piggyback on the tracing capabilities of the VM to provide labelling for prop tests. To ensure we do not interfere with normal traces, we only count traces that starts with a NUL byte as label. That convention is assumed to be known of the companion fuzz library that should then provide the labelling capabilities as a dedicated function.

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

@@ -1,13 +1,12 @@
-use chumsky::prelude::*;
-use num_bigint::BigInt;
-use ordinal::Ordinal;
-
 use super::{
     error::ParseError,
     extra::ModuleExtra,
     token::{Base, Token},
 };
 use crate::ast::Span;
+use chumsky::prelude::*;
+use num_bigint::BigInt;
+use ordinal::Ordinal;
 
 pub struct LexInfo {
     pub tokens: Vec<(Token, Span)>,
@@ -199,7 +198,8 @@ pub fn lexer() -> impl Parser<char, Vec<(Token, Span)>, Error = ParseError> {
             .or(just('"'))
             .or(just('n').to('\n'))
             .or(just('r').to('\r'))
-            .or(just('t').to('\t')),
+            .or(just('t').to('\t'))
+            .or(just('0').to('\0')),
     );
 
     let string = just('@')