feat: add support for structs and member access

tests/struct_basic.test

@@ -0,0 +1,29 @@
+[code]
+foreign fn putchar(c: i32) -> i32;
+
+struct Point {
+    x: i32,
+    y: i32
+}
+
+fn print_num(n: i32) {
+    // Simple hack to print a 2-digit number for testing
+    putchar(48 + (n / 10));
+    putchar(48 + (n % 10));
+    putchar(10); // newline
+}
+
+fn main() -> i32 {
+    let p = Point { x: 40, y: 2 };
+    
+    // 40 + 2 = 42
+    print_num(p.x + p.y);
+    
+    return 0;
+}
+
+[expected_return_code]
+0
+
+[expected_output]
+42