docstr: Save model to checkpoint but only on master process.
code: def save_lr_scheduler(
      self, lr_scheduler: LRScheduler, checkpoint: str
  ):
      """
      Save model to checkpoint but only on master process.
      """
      if self.coordinator.is_master():
          super().save_lr_scheduler(lr_scheduler, checkpoint)
  
imports: from typing import Callable, Iterator, List, Optional, Tuple
  import torch.nn
  from torch.nn.parallel import DistributedDataParallel
  from torch.optim import Optimizer
  from torch.optim.lr_scheduler import _LRScheduler
  from torch.utils.data import DataLoader
  from colossalai.checkpoint_io import CheckpointIO, GeneralCheckpointIO
  from colossalai.cluster import DistCoordinator
  from colossalai.interface import ModelWrapper, OptimizerWrapper
  from .dp_plugin_base import DPPluginBase
label_desc: Use image node_id 6 for calling the TorchDDPCheckpointIO obj's underlying member method code with example usage: obj.save_lr_scheduler(lr_scheduler, checkpoint) without return types