improve intial parameters guess Lorentzian fit

[RoyStegeman]

closes #1408

The fits in #1408 that before failed now pass.

The background was made linear in an earlier PR. In this PR we heavily rely on the assumption of a linear background to make the guesses for the initial parameters so it is stable only up to a point where the background is linear enough.

Specifically what changed are the following things:

• the linear background consisting of offset and slope is now estimated from the endpoints of the frequency domain. This linear function is subtracted before peak detection, so argmax/argmin operate on the residual signal.
• sigma is now derived from the half-maximum width of the peak after subtracting the linear background from the data. Before the distance between argmax and argmin of the raw data was used, which is much less stable.
• uncertainties are no longer passed to the fit function since uncertainties in a spectroscopy are largely unnecessary overhead. Bounds have been added to constrain the fit parameters.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.38%. Comparing base (0db1245) to head (a5656ec).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1492      +/-   ##
==========================================
- Coverage   94.43%   94.38%   -0.06%     
==========================================
  Files         136      136              
  Lines       10662    10669       +7     
==========================================
+ Hits        10069    10070       +1     
- Misses        593      599       +6     

Flag	Coverage Δ
unittests	94.38% <100.00%> (-0.06%)	⬇️

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

Files with missing lines	Coverage Δ
src/qibocal/protocols/utils.py	92.03% <100.00%> (-0.37%)	⬇️

... and 4 files with indirect coverage changes

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[alecandido]

The first two comments are stylistic.
The other two need to be addressed in a separate PR. But, if you agree with them, better to write them down in suitable issues immediately