[FEATURE] Replace the FastAI notebook by a cartesian product with PyTorch and remove the FastAI dependency

[miguelgfierro]

Description

We had some issues with the FastAI dependency #2182. And realised that the fastai notebook is just a fancy wrapper on PyTorch cartesian product between user and item embeddings.
https://github.com/recommenders-team/recommenders/blob/main/examples/00_quick_start/fastai_movielens.ipynb

Expected behavior with the suggested feature

We want replace the FastAI notebook with a PyTorch version

Willingness to contribute

• Yes, I can contribute for this issue independently.
• Yes, I can contribute for this issue with guidance from Recommenders community.
• No, I cannot contribute at this time.

Other Comments

Related to #1713

[miguelgfierro]

IDEA: I'm sure ChatGPT can translate the notebook to PyTorch

[rohan-rajput-ai]

@miguelgfierro I am unclear with the requirements. Do we just want to replace the Cartesian product or we want to completely replace fast-ai with the PyTorch?

[miguelgfierro]

@rohan-rajput-ai the idea is to remove all the code related to FastAI, and replace it with the underlying PyTorch. The output of this work needs to be a remade notebook, the removal of https://github.com/recommenders-team/recommenders/blob/main/recommenders/models/fastai/fastai_utils.py and the removal of the fastai dependency https://github.com/recommenders-team/recommenders/blob/main/setup.py#L54.

If you need to create any function, feel free to create a pytorch_utils.py file.