feat: initial parallel impl

src/engine/test.rs

@@ -2,7 +2,7 @@
 
 extern crate test;
 
-use hashbrown::HashMap;
+use std::collections::BTreeMap;
 
 use test::{Bencher, black_box};
 
@@ -23,12 +23,7 @@ fn test_expr(expr: &str, expected: Value) {
 macro_rules! map {
     ($($k:expr => $v:expr),*) => {
         {
-            #[allow(unused_mut)]
-            let mut m = HashMap::new();
-            $(
-                m.insert($k, $v);
-            )*
-            m
+            BTreeMap::from([$(($k, $v),)*])
         }
     };
 }