Introduce mutation testing

[martintmk]

The issue or feature being addressed

This PR adds the mutation testing that verifies the quality of the unit tests written.

See https://stryker-mutator.io/ for more details.

Details on the issue fix or feature implementation

No new tests added, just introdution of mutation gate. The current mutation score is 72, and new PRs that add features cannot fall below this threshold. Over time the score should increase by adding more through tests.

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 #1031 (0689041) into main (a399bd1) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1031   +/-   ##
=======================================
  Coverage   71.45%   71.45%           
=======================================
  Files         137      137           
  Lines        3745     3745           
  Branches      748      748           
=======================================
  Hits         2676     2676           
  Misses        864      864           
  Partials      205      205           

Flag	Coverage Δ
linux	71.45% <ø> (ø)
macos	71.45% <ø> (ø)
windows	71.45% <ø> (ø)

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[martincostello]

I'm on vacation until Monday, I'll take a look then.