feat: expand standard library with Math module and new functions

- Add Math module: abs, min, max, sqrt, pow, floor, ceil, round
- Add List functions: isEmpty, find, any, all, take, drop
- Add String functions: startsWith, endsWith, toUpper, toLower, substring
- Add 12 tests for new standard library functions

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/main.rs

@@ -1377,6 +1377,110 @@ c")"#;
             assert!(result.is_err());
             assert!(result.unwrap_err().contains("downgrade"));
         }
+
+        // Math module tests
+        #[test]
+        fn test_math_abs() {
+            let (result, _) = run_with_effects("let x = Math.abs(-42)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "42");
+            let (result, _) = run_with_effects("let x = Math.abs(42)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "42");
+        }
+
+        #[test]
+        fn test_math_min_max() {
+            let (result, _) = run_with_effects("let x = Math.min(3, 7)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "3");
+            let (result, _) = run_with_effects("let x = Math.max(3, 7)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "7");
+        }
+
+        #[test]
+        fn test_math_sqrt() {
+            let (result, _) = run_with_effects("let x = Math.sqrt(16)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "4");
+        }
+
+        #[test]
+        fn test_math_pow() {
+            let (result, _) = run_with_effects("let x = Math.pow(2, 10)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "1024");
+        }
+
+        #[test]
+        fn test_math_floor_ceil_round() {
+            let (result, _) = run_with_effects("let x = Math.floor(3.7)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "3");
+            let (result, _) = run_with_effects("let x = Math.ceil(3.2)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "4");
+            let (result, _) = run_with_effects("let x = Math.round(3.5)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "4");
+        }
+
+        // List module additional functions
+        #[test]
+        fn test_list_is_empty() {
+            let (result, _) = run_with_effects("let x = List.isEmpty([])", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "true");
+            let (result, _) = run_with_effects("let x = List.isEmpty([1, 2])", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "false");
+        }
+
+        #[test]
+        fn test_list_find() {
+            let source = "let x = List.find([1, 2, 3, 4, 5], fn(x: Int): Bool => x > 3)";
+            let (result, _) = run_with_effects(source, Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "Some(4)");
+            let source = "let x = List.find([1, 2, 3], fn(x: Int): Bool => x > 10)";
+            let (result, _) = run_with_effects(source, Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "None");
+        }
+
+        #[test]
+        fn test_list_any_all() {
+            let source = "let x = List.any([1, 2, 3], fn(x: Int): Bool => x > 2)";
+            let (result, _) = run_with_effects(source, Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "true");
+            let source = "let x = List.all([1, 2, 3], fn(x: Int): Bool => x > 0)";
+            let (result, _) = run_with_effects(source, Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "true");
+            let source = "let x = List.all([1, 2, 3], fn(x: Int): Bool => x > 2)";
+            let (result, _) = run_with_effects(source, Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "false");
+        }
+
+        #[test]
+        fn test_list_take_drop() {
+            let (result, _) = run_with_effects("let x = List.take([1, 2, 3, 4, 5], 3)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "[1, 2, 3]");
+            let (result, _) = run_with_effects("let x = List.drop([1, 2, 3, 4, 5], 2)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "[3, 4, 5]");
+        }
+
+        // String module additional functions
+        #[test]
+        fn test_string_starts_ends_with() {
+            let (result, _) = run_with_effects("let x = String.startsWith(\"hello\", \"he\")", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "true");
+            let (result, _) = run_with_effects("let x = String.endsWith(\"hello\", \"lo\")", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "true");
+        }
+
+        #[test]
+        fn test_string_case_conversion() {
+            let (result, _) = run_with_effects("let x = String.toUpper(\"hello\")", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "\"HELLO\"");
+            let (result, _) = run_with_effects("let x = String.toLower(\"HELLO\")", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "\"hello\"");
+        }
+
+        #[test]
+        fn test_string_substring() {
+            let (result, _) = run_with_effects("let x = String.substring(\"hello world\", 0, 5)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "\"hello\"");
+            let (result, _) = run_with_effects("let x = String.substring(\"hello\", 2, 4)", Value::Unit, Value::Unit).unwrap();
+            assert_eq!(result, "\"ll\"");
+        }
     }
 
     // Diagnostic rendering tests