Fix Issue #332 : Shallow copy data container before each epoch

[alexbrillant]

What it is

My pull request does:

Add a shallow copy in the fit_trial_split method inside the Trainer because the pipeline could change the reference of the data inputs directly, and change the values for the next epochs.

  def fit_trial_split(
           self,
           trial_split: TrialSplit,
           train_data_container: DataContainer,
           validation_data_container: DataContainer,
           context: ExecutionContext
   ) -> TrialSplit:
       """
       Train pipeline using the training data container.
       Track training, and validation metrics for each epoch.

       :param train_data_container: train data container
       :param validation_data_container: validation data container
       :param trial_split: trial to execute
       :param context: execution context

       :return: executed trial
       """
       early_stopping = False

       for i in range(self.epochs):
           self.print_func('\nepoch {}/{}'.format(i + 1, self.epochs))

           # shallow copy here to create a new reference for the data inputs inside the data container. 
           trial_split = trial_split.fit_trial_split(train_data_container.copy(), context)
           y_pred_train = trial_split.predict_with_pipeline(train_data_container.copy(), context)
           y_pred_val = trial_split.predict_with_pipeline(validation_data_container.copy(), context)

           if self.callbacks.call(
                   trial=trial_split,
                   epoch_number=i,
                   total_epochs=self.epochs,
                   input_train=train_data_container,
                   pred_train=y_pred_train,
                   input_val=validation_data_container,
                   pred_val=y_pred_val,
                   is_finished_and_fitted=early_stopping
           ):
               break

       return trial_split