Implement Phase 6 Box reference operations in MIR/VM - RefNew/RefGet/RefSet/WeakNew/WeakLoad/Barrier*

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

test_simple_field.nyash

@@ -0,0 +1,14 @@
+// Simpler test for field access MIR
+static box Main {
+    init { obj }
+    
+    main() {
+        me.obj = "test"
+        local field_value
+        
+        // This should trigger field access parsing
+        field_value = me.obj
+        print(field_value)
+        return "Done"
+    }
+}