Optimise NewDerivedNode()

Create the new node's children without making an intermediate NodeSet

render/id.go

@@ -52,7 +52,9 @@ func ParseGroupNodeTopology(topology string) (string, string, bool) {
 
 // NewDerivedNode makes a node based on node, but with a new ID
 func NewDerivedNode(id string, node report.Node) report.Node {
-	return report.MakeNode(id).WithChildren(node.Children.Add(node))
+	result := report.MakeNode(id)
+	result.Children = node.Children.Add(node)
+	return result
 }
 
 // NewDerivedPseudoNode makes a new pseudo node with the node as a child