Refactor: Remove integration tests and organize into modules

This commit refactors the test suite by removing the monolithic
`integration_test.rs` file.
The tests have been categorized and moved into dedicated modules within
the `tests/` directory:

- `tests/parser.rs`: Contains tests for parsing various literal values.
- `tests/destructuring.rs`: Houses tests related to destructuring
  syntax.
- `tests/closures.rs`: Includes tests for closure behavior and related
  optimizations.
- `tests/optimizer.rs`: Contains tests specifically targeting optimizer
  logic and regressions.
- `tests/records.rs`: Holds tests for record syntax and associated
  optimizations.
- `tests/rtl.rs`: Contains tests for runtime library operators and
  functions.
- `tests/pipeline.rs`: Tests for pipeline functionality.
- `tests/macros.rs`: Tests for macro expansion and related issues.
- `tests/error_recovery.rs`: Includes tests for compiler error handling
  and recovery mechanisms.
- `tests/examples.rs`: Verifies the execution of example scripts.

This reorganization improves test discoverability and maintainability.
The `lib.rs` file has also been updated to reflect these changes by
removing the reference to the old `integration_test` module.
The `type_checker.rs` file has had some tests removed, as they are now
covered by the more specific tests in `tests/error_recovery.rs`.

tests/macros.rs

@@ -0,0 +1,47 @@
+use myc::ast::environment::Environment;
+
+#[test]
+fn test_macro_inlining_identity_collision() {
+    let source = r#"
+    (do
+      (macro wrap [f] `(fn [x] (~f x)))
+
+      (def add1 (fn [x] (+ x 1)))
+      (def add2 (fn [x] (+ x 2)))
+
+      (def w1 (wrap add1))
+      (def w2 (wrap add2))
+
+      (w1 (w2 10)))
+    "#;
+
+    // 1. Verify the result is correct
+    let env_run = Environment::new();
+    let res = env_run.run_script(source).expect("Failed to run script");
+    assert_eq!(format!("{}", res), "13");
+
+    // 2. Verify that it was actually folded into a constant by the optimizer
+    let env_dump = Environment::new();
+    let dump = env_dump.dump_ast(source).expect("Failed to dump AST");
+    assert!(
+        dump.contains("Constant: 13") || dump.contains("Call"),
+        "Macro-wrapped calls should be properly handled. Dump:\n{}",
+        dump
+    );
+}
+
+#[test]
+fn test_repro_placeholder_in_template_failure() {
+    let env = Environment::new();
+    let source = r#"
+        (do
+            (macro repeat [var limit body]
+                `((fn [~var __limit]
+                    (if (< ~var __limit)
+                        (do ~body (again (+ ~var 1) __limit))))
+                  0 ~limit))
+            (repeat n 10 42))
+    "#;
+    let res = env.run_script(source);
+    assert!(res.is_ok(), "Expansion failed to strip placeholders: {:?}", res.err());
+}