feat: trait 接口系统 — trait Show { fn method } + extend Trait Struct { }

test/programs/35_trait.l

@@ -0,0 +1,18 @@
+trait Show {
+    fn show(self: Self) -> void;
+}
+
+struct Point { x: i64, y: i64 }
+
+extend Show Point {
+    fn show(self: Point) -> void {
+        print_i64(self.x);
+        print_i64(self.y);
+    }
+}
+
+fn main() -> i64 {
+    let p = Point { x: 10, y: 20 };
+    p.show();
+    return 0;
+}