don't cache qblox.cluster.Cluster._modules

[RoyStegeman]

In an RB experiment the cluster is connected and disconnected multiple times. By caching we try to interact with modules that have been disconnected.

Tested that it now works.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 40.08%. Comparing base (e6f498b) to head (84fa01f).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/qibolab/_core/instruments/qblox/cluster.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1355   +/-   ##
=======================================
  Coverage   40.08%   40.08%           
=======================================
  Files         114      114           
  Lines        5596     5596           
=======================================
  Hits         2243     2243           
  Misses       3353     3353           

Flag	Coverage Δ
unittests	40.08% <0.00%> (ø)

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