Phase 8.4: Complete AST→MIR Lowering - Basic object operations implemented

Co-authored-by: moe-charm <217100418+moe-charm@users.noreply.github.com>

test_wasm_box_integration.nyash

@@ -0,0 +1,19 @@
+box SimpleData {
+    init { x, y }
+    
+    pack(a, b) {
+        me.x = a
+        me.y = b
+    }
+    
+    sum() {
+        return me.x + me.y
+    }
+}
+
+static box Main {
+    main() {
+        local data = new SimpleData(10, 20)
+        return data.sum()
+    }
+}