Reducing import overhead

[andrea-pasquale]

After talking with @stavros11 we realized that now importing qibocal takes longer than usual.
After profiling the import we discover that importing skops introduces an overhead of around 2 seconds.
Here is the profiling with skops:

This PR reduces the import time by moving skops as a relative import.
Here is the updated profiling:

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

Merging #579 (b76923d) into main (96cd4d8) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #579      +/-   ##
==========================================
- Coverage   96.02%   95.99%   -0.04%     
==========================================
  Files          90       90              
  Lines        6062     6063       +1     
==========================================
- Hits         5821     5820       -1     
- Misses        241      243       +2     

Flag	Coverage Δ
unittests	95.99% <100.00%> (-0.04%)	⬇️

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

Files	Coverage Δ
src/qibocal/fitting/classifier/qubit_fit.py	100.00% <100.00%> (+3.63%)	⬆️
src/qibocal/fitting/classifier/run.py	96.69% <ø> (ø)

... and 1 file with indirect coverage changes

[Edoardo-Pedicillo]

Thank @andrea-pasquale

[stavros11]

Thanks @andrea-pasquale. I see a decrease of 1+ sec on total execution time when I run with dummy on my machine, maybe more in the cluster.