Add chrono dependency and example files

This commit introduces the `chrono` dependency to the project, enabling
the use of time-related functionalities. Additionally, it adds several
example files (`closure.myc`, `fib.myc`, `hof.myc`) to showcase the
language's features like closures, recursion, and higher-order
functions.

The `Cargo.lock` and `Cargo.toml` files have been updated to reflect the
new dependency. The `integration_test.rs` file now includes a test to
run all `.myc` files found in the `examples` directory, ensuring their
correctness. The `main.rs` file has also been updated to load and
display these examples in the UI.

src/integration_test.rs

@@ -6,8 +6,9 @@ mod tests {
     use crate::ast::compiler::binder::Binder;
     use crate::ast::vm::VM;
     use crate::ast::types::Value;
-
     use crate::ast::nodes::UntypedKind;
+    use crate::ast::environment::Environment;
+    use std::fs;
 
     #[test]
     fn test_parse_integer_constant() {
@@ -89,4 +90,39 @@ mod tests {
             Err(e) => panic!("VM Error: {}", e),
         }
     }
+
+    #[test]
+    fn test_examples() {
+        let entries = fs::read_dir("examples").expect("Could not read examples directory");
+        for entry in entries {
+            let entry = entry.expect("Invalid entry");
+            let path = entry.path();
+            if path.extension().map_or(false, |ext| ext == "myc") {
+                let content = fs::read_to_string(&path).expect("Could not read file");
+                
+                // Skip benchmarks during normal functional tests
+                if content.contains(";; Benchmark") {
+                    continue;
+                }
+
+                // Find expected output tag: ;; Output: <value>
+                let expected_output = content.lines()
+                    .find(|line| line.starts_with(";; Output:"))
+                    .map(|line| line.replace(";; Output:", "").trim().to_string());
+
+                if let Some(expected) = expected_output {
+                    let env = Environment::new();
+                    let result = env.run_script(&content);
+                    
+                    match result {
+                        Ok(val) => {
+                            let val_str = format!("{}", val);
+                            assert_eq!(val_str, expected, "Example {:?} failed: expected {}, got {}", path, expected, val_str);
+                        }
+                        Err(e) => panic!("Example {:?} failed with error: {}", path, e),
+                    }
+                }
+            }
+        }
+    }
 }