CI and lint improvements

[akx]

The usual modernization!

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.

Please upload report for BASE (master@dde6a11). Learn more about missing BASE report.

Files	Patch %	Lines
cavalry/timing.py	33.33%	2 Missing ⚠️
cavalry/db_django2.py	50.00%	1 Missing ⚠️
cavalry/db_django3.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #12   +/-   ##
=========================================
  Coverage          ?   88.95%           
=========================================
  Files             ?       15           
  Lines             ?      353           
  Branches          ?        0           
=========================================
  Hits              ?      314           
  Misses            ?       39           
  Partials          ?        0           

Flag	Coverage Δ
3.10-django>=4.0	79.88% <70.58%> (?)
3.12-django>=5.0	79.88% <70.58%> (?)
3.8-django>=2.0	83.28% <70.58%> (?)
3.8-django>=3.0	79.88% <70.58%> (?)
<3	83.28% <70.58%> (?)
<4	79.88% <70.58%> (?)
<5	79.88% <70.58%> (?)
<6	79.88% <70.58%> (?)

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