Refactor optimizer with aggressive collapsing

The optimizer has been refactored to separate its phases and introduce
more aggressive collapsing capabilities.

Phase 2 (Cracking) now focuses on stateless transformations, making it
easier to reason about and potentially parallelize.

Phase 2.5 (Aggressive Collapsing) has been introduced, enabling
optimizations like:
- Beta-reduction for lambda literals.
- Cracking and inlining for constant closures.
- Folding intrinsics for constant arithmetic.
- Short-circuiting conditional expressions.

These changes aim to improve performance by reducing redundant
computations and code bloat. The maximum number of optimization passes
has also been increased to 5 to allow for more complex transformations.

src/integration_test.rs

@@ -82,9 +82,11 @@ mod tests {
 
     #[test]
     fn test_examples() {
-        let results = crate::utils::tester::run_functional_tests();
-        for res in results {
-            assert!(res.success, "Example {} failed: {}", res.name, res.message);
+        for level in 0..=2 {
+            let results = crate::utils::tester::run_functional_tests_with_level(level);
+            for res in results {
+                assert!(res.success, "Example {} failed at level {}: {}", res.name, level, res.message);
+            }
         }
     }