Use NSubstitute for mocking in tests

[skarllot]

Pull Request

The issue or feature being addressed

• [Feature request]: Replace Moq with NSubstitute #9
• Privacy issues with SponsorLink, starting from version 4.20 devlooped/moq#1372

Details on the issue fix or feature implementation

Remove all usages of Moq library and replace with NSubstitute.

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[codecov-commenter]

Codecov Report

Merging #11 (e26e6b8) into main (eac5c59) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #11   +/-   ##
=======================================
  Coverage   72.49%   72.49%           
=======================================
  Files          14       14           
  Lines         429      429           
  Branches       33       33           
=======================================
  Hits          311      311           
  Misses        112      112           
  Partials        6        6           

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