bug: renaming checkpoints

File name conflict occurs if a training is run more than once within a minute:

• In a first training campaign, three checkpoints are saved: one last.ckpt and two best checkpoints.
• On a second run within a minute, the last checkpoint is renamed with a suffix indicating its creation date YYYY-mm-dd_HH-MM, and a new last.ckpt file is added (and two new best). No error at this point, but the new last.ckpt file has the same last-modified date as the previous one.
• If the training is run again, at any point of time, the file overwrite error occurs, because last.ckpt cannot be renamed by adding the date suffix.

---------------------------------------------------------------------------
FileExistsError                           Traceback (most recent call last)
Cell In[47], line 1
----> 1 model.fit(datamodule, name_run='train_semiramis', max_epochs=20, accelerator='cpu', flag_wandb=False)

File ~\aixd\src\aixd\mlmodel\architecture\cond_ae_model.py:642, in CondAEModel.fit(self, datamodule, name_run, max_epochs, callbacks, loggers, accelerator, flag_early_stop, criteria, flag_wandb, wandb_entity, **kwargs)
    640 if os.path.exists(os.path.join(self.save_dir, self.CHECKPOINT_DIR, "last.ckpt")):
    641     date_f = self._get_file_creation_date(os.path.join(self.save_dir, self.CHECKPOINT_DIR, "last.ckpt"))
--> 642     os.rename(os.path.join(self.save_dir, self.CHECKPOINT_DIR, "last.ckpt"), os.path.join(self.save_dir, self.CHECKPOINT_DIR, "last_" + date_f + ".ckpt"))
    644 callbacks.append(
    645     ModelCheckpoint(
    646         monitor=criteria,
   (...)
    653     )
    654 )
    656 # Setup early stopping callback

FileExistsError: [WinError 183] Cannot create a file when that file already exists: 
'c:\\..\\checkpoints\\last.ckpt' -> 'c:\\..\\checkpoints\\last_2025-02-18_13-56.ckpt'

Also, for multiple runs within a minute, the best checkpoints share the same prefix for all runs.

Suggestion: change the suffix to include seconds: YYYY-mm-dd_HH-MM-SS ?