Refactor map and record representation

Replaces the use of `BTreeMap` and `HashMap` for maps and records with
`Vec<(Keyword, Value)>` and `Vec<(Keyword, StaticType)>`. This
simplifies the data structure and allows for ordered iteration, which is
important for serialization and comparison.

Also updates the `unpack` function in `vm.rs` to handle records as well
as lists when destructuring.

src/ast/compiler/type_checker.rs

@@ -309,13 +309,13 @@ impl TypeChecker {
 
             BoundKind::Map { entries } => {
                 let mut typed_entries = Vec::new();
-                let mut fields = std::collections::BTreeMap::new();
+                let mut fields = Vec::new();
                 for (k, v) in entries {
                     let kt = self.check_node(k, ctx)?;
                     let vt = self.check_node(v, ctx)?;
                     
                     if let BoundKind::Constant(crate::ast::types::Value::Keyword(kw)) = &kt.kind {
-                        fields.insert(*kw, vt.ty.clone());
+                        fields.push((*kw, vt.ty.clone()));
                     }
                     
                     typed_entries.push((kt, vt));
@@ -484,8 +484,8 @@ mod tests {
         let ty = get_ret_type(&typed);
         if let StaticType::Record(fields) = ty {
             assert_eq!(fields.len(), 2);
-            assert_eq!(fields.get(&Keyword::intern("x")), Some(&StaticType::Int));
-            assert_eq!(fields.get(&Keyword::intern("y")), Some(&StaticType::Float));
+            assert_eq!(fields[0], (Keyword::intern("x"), StaticType::Int));
+            assert_eq!(fields[1], (Keyword::intern("y"), StaticType::Float));
         } else {
             panic!("Expected Record, got {:?}", ty);
         }