feat: higher level psf caching

[tlambert03]

this caches PSFs at a slightly higher level (make_psf) which will also include the convolution done when making a confocal psf. In order to do say, it makes NumpyAPI hashable in a way that may possible be troublesome later, but we'll cross that bridge when we come to it

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.99%. Comparing base (5acbbb1) to head (daedf0b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #28      +/-   ##
==========================================
+ Coverage   78.87%   78.99%   +0.11%     
==========================================
  Files          36       36              
  Lines        1619     1628       +9     
==========================================
+ Hits         1277     1286       +9     
  Misses        342      342              

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