Add verbose logging when ModelCheckpoint callback is done saving ... (#21805)

* Add verbose logging when ModelCheckpoint callback is done saving a model.

This is useful for collecting information on how long model checkpointing takes, together with existing verbose logging on initiating the save.

* Update model_checkpoint.py

Updated formatting for line length.

Author: kathyfan

keras/src/callbacks/model_checkpoint.py

@@ -283,6 +283,11 @@ def _save_model(self, epoch, batch, logs):
                     self.model.save_weights(filepath, overwrite=True)
                 else:
                     self.model.save(filepath, overwrite=True)
+                if self.verbose > 0:
+                    io_utils.print_msg(
+                        f"\nEpoch {epoch + 1}: "
+                        f"finished saving model to {filepath}"
+                    )
         except IsADirectoryError:  # h5py 3.x
             raise IOError(
                 "Please specify a non-directory filepath for "