Implemented lazy evaluation for minor_servos and active_surface.usd

[giuseppe-carboni]

With this modification, we got rid of some threads that used to update positions in background, so that simulators are less computational-intense, requiring less CPU.
Also the acu simulator thread sample_rate was reduced.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (87f7e8f) to head (91bf840).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #360   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           39        39           
  Lines         8377      8381    +4     
=========================================
+ Hits          8377      8381    +4     

Files with missing lines	Coverage Δ
simulators/active_surface/__init__.py	100.00% <ø> (ø)
simulators/active_surface/usd.py	100.00% <100.00%> (ø)
simulators/acu/__init__.py	100.00% <100.00%> (ø)
simulators/minor_servos/__init__.py	100.00% <100.00%> (ø)
simulators/utils.py	100.00% <100.00%> (ø)

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