Creation of qibo.models.encodings and implementation of unary_encoder

[renatomello]

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files	Coverage Δ
src/qibo/models/__init__.py	100.00% <100.00%> (ø)
src/qibo/models/encodings.py	100.00% <100.00%> (ø)

📢 Thoughts on this report? Let us know!.

[MatteoRobbiati]

Thank you, it is fine for me.
Just a question, I noticed the notation is slightly different from the paper you cite in the docstrings. Did you apply these modifications in order to correctly deploy the data loader?
It perfectly works btw, so it sounds good to me.

[renatomello]

Thank you, it is fine for me. Just a question, I noticed the notation is slightly different from the paper you cite in the docstrings. Did you apply these modifications in order to correctly deploy the data loader? It perfectly works btw, so it sounds good to me.

I don't know which part exactly you're referring to, but it's probably just personal preference.

[stavros11]

Minor comments, looks good to merge as it is. The only thing that is slightly weird is that this is exposed as a model, but the name follows different convention than other models. Some users may expect from qibo.models import UnaryEncoder. I get that you are following the function naming convention so it should be fine to keep as it is.