Update import from lightning.pytorch (#409)

* update import
* Remove unnecessary import return type

---------

Co-authored-by: Filippo Olivo <filippo@filippoolivo.com>

pina/callbacks/adaptive_refinment_callbacks.py

@@ -1,7 +1,7 @@
 """PINA Callbacks Implementations"""
 
 import torch
-from pytorch_lightning.callbacks import Callback
+from lightning.pytorch.callbacks import Callback
 from ..label_tensor import LabelTensor
 from ..utils import check_consistency
 

pina/callbacks/optimizer_callbacks.py

@@ -1,6 +1,6 @@
 """PINA Callbacks Implementations"""
 
-from pytorch_lightning.callbacks import Callback
+from lightning.pytorch.callbacks import Callback
 import torch
 from ..utils import check_consistency
 

pina/callbacks/processing_callbacks.py

@@ -1,11 +1,11 @@
 """PINA Callbacks Implementations"""
 
-from pytorch_lightning.core.module import LightningModule
-from pytorch_lightning.trainer.trainer import Trainer
+from lightning.pytorch.core.module import LightningModule
+from lightning.pytorch.trainer.trainer import Trainer
 import torch
 import copy
 
-from pytorch_lightning.callbacks import Callback, TQDMProgressBar
+from lightning.pytorch.callbacks import Callback, TQDMProgressBar
 from lightning.pytorch.callbacks.progress.progress_bar import (
     get_standard_metrics,
 )