Names convention

[FilippoOlivo]

Currently, the library has several inconsistencies in class and module names. I started this discussion to establish a naming convention moving forward, ensuring a clearer and more consistent structure. The main issues that @ndem0 and I have identified are:

1. Module inconsistency: Some module names are plural (e.g., solvers and callbacks), while others are singular. We need to decide on a consistent approach.
2. Attribute naming in solver classes: For example, should we keep _pina_models, or is it better renaming it to _models?

[ndem0]

To keep the code general and avoid repetitive information, I would keep the singular form for all the submodules/modules (so solver, pinn, callback, ...) and avoid the pina keyword in the attributes/methods.

Also, should we go for the long name for classes? Mainly for sake of clarity, I slightly prefer the long name (and the user can make the acronym at the import level, eg from pina.model import FourierNeuralOperator as FNO).

What do you think?

[dario-coscia]

I agree on both, let's keep the singular form as the standard and long class names (it is clearer IMHO).

Also, I agree with @FilippoOlivo to remove _pina_...

[GiovanniCanali]

I totally agree with the suggestions. I would extend this convention to file names as well. For example, instead of naming a file fno.py, I would prefer fourier_neural_operator.py. @FilippoOlivo

[dario-coscia]

Closing the discussion, the singular is used in the 0.2 version (introduce in #457)