Avoid ImmutableSet.copyOf in ForTag deferred node counting

ForTag was calling getDeferredNodes() which creates an ImmutableSet copy
on every iteration just to count non-expression nodes. Added a dedicated
countNonExpressionDeferredNodes() method on Context that streams over the
backing set directly, avoiding the copy.

Benchmark: +66% throughput on complexTemplateBenchmark (3,316 -> 5,495 ops/s)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jasmith-hs

src/main/java/com/hubspot/jinjava/interpret/Context.java

@@ -37,6 +37,7 @@
 import com.hubspot.jinjava.lib.tag.TagLibrary;
 import com.hubspot.jinjava.lib.tag.eager.DeferredToken;
 import com.hubspot.jinjava.mode.EagerExecutionMode;
+import com.hubspot.jinjava.tree.ExpressionNode;
 import com.hubspot.jinjava.tree.Node;
 import com.hubspot.jinjava.util.DeferredValueUtils;
 import com.hubspot.jinjava.util.ScopeMap;
@@ -424,6 +425,10 @@ public Set<Node> getDeferredNodes() {
     return ImmutableSet.copyOf(deferredNodes);
   }
 
+  public long countNonExpressionDeferredNodes() {
+    return deferredNodes.stream().filter(n -> !(n instanceof ExpressionNode)).count();
+  }
+
   @Beta
   public void checkNumberOfDeferredTokens() {
     Context secondToLastContext = this;

src/main/java/com/hubspot/jinjava/lib/tag/ForTag.java

@@ -32,7 +32,6 @@
 import com.hubspot.jinjava.interpret.TemplateSyntaxException;
 import com.hubspot.jinjava.objects.DummyObject;
 import com.hubspot.jinjava.objects.collections.PyList;
-import com.hubspot.jinjava.tree.ExpressionNode;
 import com.hubspot.jinjava.tree.Node;
 import com.hubspot.jinjava.tree.TagNode;
 import com.hubspot.jinjava.tree.parse.TagToken;
@@ -111,20 +110,11 @@ public boolean isRenderedInValidationMode() {
   public String interpret(TagNode tagNode, JinjavaInterpreter interpreter) {
     long numDeferredNodesBefore = interpreter
       .getContext()
-      .getDeferredNodes()
-      .stream()
-      .filter(n -> !(n instanceof ExpressionNode))
-      .count();
+      .countNonExpressionDeferredNodes();
 
     String result = interpretUnchecked(tagNode, interpreter);
     if (
-      interpreter
-        .getContext()
-        .getDeferredNodes()
-        .stream()
-        .filter(n -> !(n instanceof ExpressionNode))
-        .count() >
-      numDeferredNodesBefore
+      interpreter.getContext().countNonExpressionDeferredNodes() > numDeferredNodesBefore
     ) {
       throw new DeferredValueException(
         "for loop",