Proper name for fit functions

[andrea-pasquale]

Closes #393

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.
• Compatibility with Qibo modules (Please edit this section if the current pull request is not compatible with the following branches).
  • Qibo: master
  • Qibolab: main
  • Qibolab_platforms_qrc: main

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.36%. Comparing base (b0c0ef7) to head (7f83710).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #875      +/-   ##
==========================================
- Coverage   97.40%   97.36%   -0.05%     
==========================================
  Files         115      115              
  Lines        8645     8645              
==========================================
- Hits         8421     8417       -4     
- Misses        224      228       +4     

Flag	Coverage Δ
unittests	97.36% <100.00%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...cal/protocols/two_qubit_interaction/cz_virtualz.py	93.91% <100.00%> (ø)

... and 2 files with indirect coverage changes