Update dependency NUnit to v4

[kayoub5]

See https://docs.nunit.org/articles/nunit/release-notes/Nunit4.0-MigrationGuide.html

NUnit.Analyzer was used to perform Assert migration automatically

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0128405) 82.81% compared to head (8aed9d2) 82.85%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #493      +/-   ##
==========================================
+ Coverage   82.81%   82.85%   +0.03%     
==========================================
  Files          51       51              
  Lines        2823     2823              
  Branches      312      312              
==========================================
+ Hits         2338     2339       +1     
  Misses        362      362              
+ Partials      123      122       -1     

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