Add Rhino tests and refactor current ones

[adamhathcock]

• Structs are now Fake classes to work with mocking
• add MoqTest base class to get rid of some of the testing repeats needs https://github.com/specklesystems/speckle-sharp/pull/3549

[adamhathcock]

Will put this on new repo: https://github.com/specklesystems/speckle-sharp-connectors