Address further Sidekick review feedback

- Use instanceof pattern matching in NoInvokeELContext to avoid bare ClassCastException when delegate doesn't implement HasInterpreter
- Guard against null JinjavaInterpreter.getCurrent() in SizeLimitingPySet.checkSize

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

Author: jasmith-hs

src/main/java/com/hubspot/jinjava/el/NoInvokeELContext.java

@@ -35,6 +35,9 @@ public VariableMapper getVariableMapper() {
 
   @Override
   public JinjavaInterpreter interpreter() {
-    return ((HasInterpreter) delegate).interpreter();
+    if (delegate instanceof HasInterpreter hasInterpreter) {
+      return hasInterpreter.interpreter();
+    }
+    return JinjavaInterpreter.getCurrent();
   }
 }

src/main/java/com/hubspot/jinjava/objects/collections/SizeLimitingPySet.java

@@ -50,9 +50,11 @@ private void checkSize(int newSize) {
       throw new CollectionTooBigException(newSize, maxSize);
     } else if (!hasWarned && newSize >= maxSize * 0.9) {
       hasWarned = true;
-      JinjavaInterpreter
-        .getCurrent()
-        .addError(
+      JinjavaInterpreter current = JinjavaInterpreter.getCurrent();
+      if (current == null) {
+        return;
+      }
+      current.addError(
           new TemplateError(
             ErrorType.WARNING,
             ErrorReason.COLLECTION_TOO_BIG,