[NFC] polish colossalai/auto_parallel/offload/amp_optimizer.py code style (#4255)

colossalai/auto_parallel/offload/amp_optimizer.py

-from typing import Dict, Tuple
 from enum import Enum
+from typing import Dict, Tuple
+
 import torch
 from torch.optim import Optimizer
 
+from colossalai.amp.naive_amp.grad_scaler import DynamicGradScaler
 from colossalai.logging import get_dist_logger
 from colossalai.nn.optimizer import ColossalaiOptimizer
-from colossalai.amp.naive_amp.grad_scaler import DynamicGradScaler
 from colossalai.utils import get_current_device
 
 from .base_offload_module import BaseOffloadModule
-from .region_manager import RegionManager
 from .region import Region
+from .region_manager import RegionManager
 
 
 class OptimState(Enum):
     SCALED = 0
     UNSCALED = 1
 
-class AMPOptimizer(ColossalaiOptimizer):
 
+class AMPOptimizer(ColossalaiOptimizer):
     """
     A wrapper for Optimizer.
     Code reference: https://github.com/hpcaitech/ColossalAI/blob/main/colossalai/nn/optimizer/zero_optimizer.py