Add Ophir powermeters

[BenediktBurger]

Adds Ophir powermeters.

Several share the same commands, therefore I have a large base class and mixin classes for device groups.

[codecov]

Codecov Report

Attention: Patch coverage is 86.89956% with 30 lines in your changes are missing coverage. Please review.

Project coverage is 58.06%. Comparing base (4846672) to head (f470460).

❗ Current head f470460 differs from pull request most recent head 509cdb0

Please upload reports for the commit 509cdb0 to get more accurate results.

Files	Patch %	Lines
pymeasure/instruments/ophir/ophir_base.py	85.44%	23 Missing ⚠️
pymeasure/instruments/ophir/nova.py	83.72%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1053      +/-   ##
==========================================
- Coverage   58.48%   58.06%   -0.43%     
==========================================
  Files         262      258       -4     
  Lines       18198    17867     -331     
==========================================
- Hits        10643    10374     -269     
+ Misses       7555     7493      -62     

Flag	Coverage Δ
unittests	58.06% <86.89%> (-0.43%)	⬇️

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