[optimise] Cache atomized value of NodeProxy

Can someone who knows better than me confirm whether this is valid ?

Looks like about 7.90s —> 7.70s

exist-core/src/main/java/org/exist/dom/persistent/NodeProxy.java

@@ -51,6 +51,7 @@
 import java.io.IOException;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
+import java.util.Optional;
 import java.util.Properties;
 
 /**
@@ -112,6 +113,11 @@ public class NodeProxy implements NodeSet, NodeValue, NodeHandle, DocumentSet, C
 
     private final Expression expression;
 
+    /**
+     * Used to cache the result of {@link #atomize()}.
+     */
+    @Nullable private AtomicValue atomized = null;
+
     /**
      * Creates a new <code>NodeProxy</code> instance.
      *
@@ -758,7 +764,10 @@ public AtomicValue convertTo(final int requiredType) throws XPathException {
 
     @Override
     public AtomicValue atomize() throws XPathException {
-        return new UntypedAtomicValue(getNodeValue());
+        if (atomized == null) {
+            atomized = new UntypedAtomicValue(getNodeValue());
+        }
+        return atomized;
     }
 
     @Override