DOC/WIP: performance tips for large displays

[ZLLentz]

I think completing this would be useful.

During the EPICS codeathon (may 2022) we identified some performance scaling issues with large displays- I'd like to investigate further what kinds of tips or tools we can include to help these displays perform better.

[codecov-commenter]

Codecov Report

Merging #862 (4e3f4c7) into master (25ad437) will decrease coverage by 0.00%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #862      +/-   ##
==========================================
- Coverage   61.97%   61.97%   -0.01%     
==========================================
  Files          98       98              
  Lines       12008    12005       -3     
==========================================
- Hits         7442     7440       -2     
+ Misses       4566     4565       -1     

Impacted Files	Coverage Δ
pydm/widgets/multi_axis_viewbox.py	28.94% <0.00%> (-5.20%)	:arrow_down:
pydm/widgets/base.py	90.68% <0.00%> (+0.20%)	:arrow_up:

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[ZLLentz]

Some other ideas of performance tips to include:

• fast-running slots
• using signals as callbacks
• Qt.QueuedConnection
• How to set up custom PyDMChannel instances

[ZLLentz]

Another idea:

• How to use profiler outputs