🎨 Refector code to remove the use of both System.Text.Json and Newtonsoft.Json

[eduwardpost]

Is your feature request related to a problem? Please describe.
Both System.Text.Json and Newtonsoft.Json are used in the project (Newtonsoft as JObjects)
This is causing problems for the custom property mapper and is now preventing unit test creations

Describe the solution you'd like
Move fully to System.Text.Json this seems to be becoming the standard since dotnet 7 / dotnet 8 and is also pushed by microsoft so it should get better first citizen party support

Describe alternatives you've considered
Move fully to Newtonsoft.Json, but i'd not choose this since this is a 3th party citizen instead of a first party.