Make debugging AssertResourceFilteredCount issues easier

[rabbitfang]

• If the assert fails, it now logs which part of the filter matched or didn't.
• Refactors ResourceFilter to group the elements of each filter (test and stringer) together. This should make it easier to add new filter options in the future.

[rabbitfang]

This PR conflicts slightly with #197, which adds a DisplayIdPrefix filter option, but the conflict should be easy to resolve.

[codecov]

Codecov Report

Merging #199 (7f3dbbe) into main (9e24b89) will increase coverage by 0.48%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #199      +/-   ##
==========================================
+ Coverage   73.17%   73.66%   +0.48%     
==========================================
  Files         104      104              
  Lines        5447     5486      +39     
==========================================
+ Hits         3986     4041      +55     
+ Misses       1191     1178      -13     
+ Partials      270      267       -3     

Impacted Files	Coverage Δ
pkg/testingutil/type.go	100.00% <ø> (ø)
pkg/testingutil/chan.go	100.00% <100.00%> (ø)
pkg/testingutil/filter.go	100.00% <100.00%> (+10.34%)	⬆️
pkg/testingutil/model.go	51.42% <100.00%> (+15.16%)	⬆️

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