[proposal] Backend for Keras 3

[thoth291]

It looks like Keras 3 is looking for some alternative backends and they even consider using Mojo for an alternative.

I would love to see Keras 3 backend written in LPython - joining forces + gaining audience.

https://keras.io/keras_3/#:~:text=Q%3A%20Will%20you%20add%20more%20backends%20in%20the%20future%3F%20What%20about%20framework%20XYZ%3F

[certik]

I think that would be great. Let me know if you want to meet to discuss more.