Refactor: Move utils to separate module

Moves `PathTracker` and `UsageInfo` to the `utils` module to improve
code organization.

src/ast/compiler/optimizer/engine.rs

@@ -5,12 +5,13 @@ use crate::ast::nodes::Node;
 use crate::ast::types::{Purity, Value};
 use crate::ast::vm::Closure;
 use std::cell::RefCell;
-use std::collections::{HashMap, HashSet};
+use std::collections::HashMap;
 use std::rc::Rc;
 
-use super::substitution_map::{SubstitutionMap, UsageInfo};
+use super::substitution_map::SubstitutionMap;
 use super::folder::Folder;
 use super::inliner::Inliner;
+use super::utils::{PathTracker, UsageInfo};
 
 pub struct Optimizer {
     pub enabled: bool,
@@ -20,34 +21,6 @@ pub struct Optimizer {
     pub lambda_registry: Option<Rc<RefCell<HashMap<GlobalIdx, AnalyzedNode>>>>,
 }
 
-struct PathTracker {
-    inlining_depth: usize,
-    inlining_stack: HashSet<GlobalIdx>,
-    identity_stack: HashSet<crate::ast::types::Identity>,
-}
-
-impl PathTracker {
-    fn new() -> Self {
-        Self {
-            inlining_depth: 0,
-            inlining_stack: HashSet::new(),
-            identity_stack: HashSet::new(),
-        }
-    }
-
-    fn enter_lambda(&mut self, identity: &crate::ast::types::Identity) -> bool {
-        if self.identity_stack.contains(identity) {
-            return false;
-        }
-        self.identity_stack.insert(identity.clone());
-        true
-    }
-
-    fn exit_lambda(&mut self, identity: &crate::ast::types::Identity) {
-        self.identity_stack.remove(identity);
-    }
-}
-
 impl Optimizer {
     pub fn new(enabled: bool) -> Self {
         Self {