test: add test case for uncaught throw in interpreter

This adds a test case to explicitly verify the error bubbling path
for a throw statement that is executed without an enclosing try-catch
block in the AST. This satisfies the testing requirement in
interpreter_tests.rs for uncaught throws.

Co-authored-by: Tcode-Motion <188012755+Tcode-Motion@users.noreply.github.com>

Author: google-labs-jules[bot]

runtime/interpreter/tests/interpreter_tests.rs

@@ -194,6 +194,21 @@ try {
     assert_eq!(val, RuntimeValue::Str("critical exception".to_string()));
 }
 
+#[test]
+fn test_interpreter_uncaught_throw() {
+    let source = r#"
+throw "uncaught exception"
+"#;
+    let res = run_source(source);
+    assert!(res.is_err());
+    let err = res.unwrap_err();
+    assert_eq!(err.message, "uncaught exception");
+    match err.kind {
+        RuntimeErrorKind::UserError(msg) => assert_eq!(msg, "uncaught exception"),
+        _ => panic!("Expected UserError"),
+    }
+}
+
 #[test]
 fn test_v108_runtime_compatibility() {
     let source = r#"