More consistent use of test library

[gammazero]

Use the require consistently in test code. In some test code it is used in some places and not others.
Use the require test utility library in more test code in general to reduce code and have more consistent error messages.

[codecov-commenter]

Codecov Report

Patch coverage: 80.76% and project coverage change: +1.13 🎉

Comparison is base (58cc78b) 54.18% compared to head (9687408) 55.31%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1392      +/-   ##
==========================================
+ Coverage   54.18%   55.31%   +1.13%     
==========================================
  Files         150      150              
  Lines       15345    15239     -106     
==========================================
+ Hits         8314     8430     +116     
+ Misses       6114     5954     -160     
+ Partials      917      855      -62     

Impacted Files	Coverage Δ
server/ingest/test/test.go	45.86% <42.30%> (+19.67%)	⬆️
dagsync/test/util.go	96.96% <100.00%> (+16.87%)	⬆️
server/finder/test/test.go	95.87% <100.00%> (+32.33%)	⬆️

... and 3 files with indirect coverage changes

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