test: Numpy 2.0 compatibility

[effigies]

Tell numpy to use legacy formatting during tests. This changes annoying things like numpy.float32(0.0) to 0.0 again.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.56%. Comparing base (c980e13) to head (449edfa).
Report is 26 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #127      +/-   ##
==========================================
+ Coverage   59.24%   59.56%   +0.31%     
==========================================
  Files          20       20              
  Lines        2238     2238              
  Branches      398      398              
==========================================
+ Hits         1326     1333       +7     
+ Misses        814      809       -5     
+ Partials       98       96       -2     

Flag	Coverage Δ
unittests	59.40% <ø> (?)

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