Train in native PyTorch

[Trainer] takes care of the training loop and allows you to fine-tune a model in a single line of code. For users who prefer to write their own training loop, you can also fine-tune a 🤗 Transformers model in native PyTorch.
At this point, you may need to restart your notebook or execute the following code to free some memory:
py
del model
del trainer
torch.cuda.empty_cache()
Next, manually postprocess tokenized_dataset to prepare it for training.