Update non-package projects to dotnet 6 + increase testing

Increase unit test coverage Remove redundant / duplicated code Minor refactorings Should also resolve the outstanding PRs from dependabot

Please let me know if you want to split these into separate PRs

@awelburn, really sorry, I missed the notification for this PR.

Most of the changes I'm happy with, so great work 🙂 I have left a comment on a class that was removed though.

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I know it's been a while, so if you don't want to look at resolving the comment, let me know and I'll make the change 🙂