Evaluate the sweetspot closest to the center of bias interval

[Edoardo-Pedicillo]

This PR solves #1067 and improves the documentation for qubit flux dependency.

By re-executing the fit of the report in the issue, this is the final result http://login.qrccluster.com:9000/nR6UbuqNQB2FTe7hRsI2Ww==/

EDIT: updated version with the sweetspot plot http://login.qrccluster.com:9000/E8Q42n_PRhyPS3WZbCLDVg==/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.32%. Comparing base (78a0bbb) to head (8f21d94).
Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1068   +/-   ##
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  Coverage   97.32%   97.32%           
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  Files         124      124           
  Lines        9894     9896    +2     
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+ Hits         9629     9631    +2     
  Misses        265      265           

Flag	Coverage Δ
unittests	97.32% <100.00%> (+<0.01%)	⬆️

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

Files with missing lines	Coverage Δ
...protocols/flux_dependence/qubit_flux_dependence.py	97.39% <100.00%> (+0.02%)	⬆️
...l/protocols/flux_dependence/resonator_crosstalk.py	96.89% <ø> (ø)
...ocols/flux_dependence/resonator_flux_dependence.py	98.31% <100.00%> (ø)
src/qibocal/protocols/flux_dependence/utils.py	98.96% <100.00%> (+0.01%)	⬆️

... and 3 files with indirect coverage changes

[andrea-pasquale]

Thanks @Edoardo-Pedicillo

[andrea-pasquale]

The corresponding attribute for resonator flux dependence is resonator_freq.
Either we change the name of the attribute in the corresponding resonator class or we need to add an if statement here.

[Edoardo-Pedicillo]

I prefer the first option, since having a resonator_freq attribute in ResonatoFluxResults is a bit redundant.