Try composition instead of inheritance

Author: saki7

test/rvariant/truly_recursive_test.cpp

@@ -143,9 +143,19 @@ struct NodeArray;
 
 using Node = iris::rvariant<int, iris::recursive_wrapper<NodeArray>>;
 
-struct NodeArray : std::vector<Node>
+struct NodeArray
 {
-    using std::vector<Node>::vector;
+    std::vector<Node> nodes;
+
+    bool operator==(NodeArray const& other) const
+    {
+        return nodes == other.nodes;
+    }
+
+    auto operator<=>(NodeArray const& other) const
+    {
+        return nodes <=> other.nodes;
+    }
 };
 
 } // anonymous