code: def register_metrics_handler(cls):
      METRICS_HANDLER_CLASSES_TEST_REGISTRY.add(cls)
      return cls
  
imports: from parlai.core.message import Message
  from parlai.core.metrics import Metric, AverageMetric
  from parlai.core.tod.tod_core import STANDARD_DONE
  from typing import Dict, List, Optional
label_desc: Use image node_id 1 for calling a global function with example usage: register_metrics_handler(cls) and returns: cls