Fix linting errors and refactor code

[hasnainmohiuddin]

• [✅] I have provided code that clearly demonstrates the bug and that only works correctly when applying this fix
• [✅] I have added suitable tests demonstrating a fixed bug or new/changed feature to the test suite in tests/
• [✅] I have properly documented new or changed features in the documentation or in the docstrings
• [✅] I have properly explained unusual or unexpected code in the comments around it

[Cokral]

I think the linting errors you are refering to were fixed already, as CI on master runs nicely.

[Cokral]

What is the benefit of doing this? numpy, and other dependencies are clearly stated in the pyproject.toml file so I think adding this is overkill.

Maybe I am missing some other benefit?

[Zulko]

Looks like there is more than code refactoring and style linting in this MR. Maybe submit it as smaller MRs?