Write date in checkpoint file (#5514)

* write date in checkpoint file

write date in checkpoint file

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* isoformat

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

train.py

 import sys
 import time
 from copy import deepcopy
+from datetime import datetime
 from pathlib import Path
 
 import numpy as np
                         'ema': deepcopy(ema.ema).half(),
                         'updates': ema.updates,
                         'optimizer': optimizer.state_dict(),
-                        'wandb_id': loggers.wandb.wandb_run.id if loggers.wandb else None}
+                        'wandb_id': loggers.wandb.wandb_run.id if loggers.wandb else None,
+                        'date': datetime.now().isoformat()}
 
                 # Save last, best and delete
                 torch.save(ckpt, last)