Audit

[alecandido]

This is a meta-issue, to monitor other ones related to the refactoring of various parts of the eko code.

In particular, here only the code that has been left into the eko package (and strictly related, like the respective tests) is of interest.
The goal is to reconsider the choices we made when the project was much younger, in light of the new developments, and to improve maintainability.

No new feature will be tracked.

• eko.evolution_operator and eko.member Reorganize evol ops #206
• eko.scale_variations
• eko.kernels (mostly because to better integrate QED) Reorganize split between Operator and Kernels #224
• eko.couplings
• and their tests Refactor couplings tests and benchmark #184
• eko.basis_rotation
• eko.msbar_masses
• drop legacy code, and start from clean