Really disconnect QM (0.1)

[stavros11]

Removes the self.manager reference, so that QM is not available after calling platform.disconnect().

Note that in 0.2 this is already fixed:

qibolab/src/qibolab/_core/instruments/qm/controller.py

Line 239 in 13c94d4

self.manager = None

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 69.85%. Comparing base (cc64ee1) to head (e46b12c).
Report is 3 commits behind head on 0.1.

Files with missing lines	Patch %	Lines
src/qibolab/instruments/qm/controller.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              0.1    #1107      +/-   ##
==========================================
- Coverage   69.88%   69.85%   -0.04%     
==========================================
  Files          64       64              
  Lines        6880     6883       +3     
==========================================
  Hits         4808     4808              
- Misses       2072     2075       +3     

Flag	Coverage Δ
unittests	69.85% <0.00%> (-0.04%)	⬇️

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