fix kernel based weights being generated multiple times

[hay-k]

Fixes the issue described here

Previously, when qubit kernels were available, the calculated weight was not stored in the weights dict, hence when needed it was recalculated, resulting into different laboneq pulse objects (even though the contained data was exactly the same, the IDs of the objects were different), causing the mentioned issue.

[Jacfomg]

Thanks, you are right about what you mentioned on the issue

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 70.27%. Comparing base (9bbbbe8) to head (c6704ad).
Report is 2 commits behind head on 0.1.

Files	Patch %	Lines
src/qibolab/instruments/zhinst/executor.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              0.1    #1000      +/-   ##
==========================================
+ Coverage   70.24%   70.27%   +0.03%     
==========================================
  Files          64       64              
  Lines        6701     6698       -3     
==========================================
  Hits         4707     4707              
+ Misses       1994     1991       -3     

Flag	Coverage Δ
unittests	70.27% <75.00%> (+0.03%)	⬆️

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[andrea-pasquale]

Thanks, now also qiboteam/qibolab_platforms_qrc#167 works for me.
With the loaded kernels the fidelity drops which makes sense
http://login.qrccluster.com:9000/5SWd0VlIQv6sucWCVu6KEw==