class_docstr: callback to be used with LightningTrainer and torchmetric
  Warning: 'optimizer.enable_state_sharding=True' is not supported
code: def on_train_start(
      self, trainer: Trainer, pl_module: LightningModule
  ):
      registry.register("current_epoch", trainer.current_epoch)
      self.lightning_trainer.torchmetrics.reset()
  
imports: import logging
  from typing import Any, Dict, List, Optional
  import torch
  from mmf.common.registry import registry
  from mmf.common.sample import SampleList
  from mmf.utils.timer import Timer
  from pytorch_lightning import LightningModule, Trainer
  from pytorch_lightning.callbacks.base import Callback
label_desc: Use image node_id 2 for calling the LightningTorchMetricsCallback obj's underlying member method code with example usage: obj.on_train_start(trainer, pl_module) without return types