code: def step_scheduler(
      optimizer: Optimizer, steps: List[int], lr_decay: float
  ) -> MultiStepLR:
      return MultiStepLR(optimizer, milestones=steps, gamma=lr_decay)
  
file_path: pytorch_geometric/torch_geometric/graphgym/optim.py
imports: from dataclasses import dataclass, field
  from typing import Any, Iterator, List, Optional
  from torch.nn import Parameter
  from torch.optim import SGD, Adam, Optimizer
  from torch.optim.lr_scheduler import CosineAnnealingLR, MultiStepLR, StepLR
  import torch_geometric.graphgym.register
  from torch_geometric.graphgym.config import from_config
label_desc: Use image node_id 5 for calling a global function with example usage: step_scheduler(optimizer, steps, lr_decay) and returns: MultiStepLR