Upgrade NUnit to version 4

[Meir017]

Feature request type

enhancement

Is your feature request related to a problem? Please describe

NUnit 4 has many improvements compared to NUnit 3, specifically the error messages are much better, see https://docs.nunit.org/articles/nunit/Towards-NUnit4.html

Describe the solution you'd like

Using NUnit's 4 code-fixers to replace the current asserts used with the NUnit API, see https://docs.nunit.org/articles/nunit-analyzers/NUnit-Analyzers.html#assertion-rules-nunit2001---

Describe alternatives you've considered

No response

Additional context

No response