This is an adaptation of https://github.com/zoho/books-dotnet-wrappers for campatibility with .net6.
- replacement of the use of Newtonsoft Json with the native JsonSerializer (System.Text.Json)
- introduced async await in most places
This is an adaptation of https://github.com/zoho/books-dotnet-wrappers for campatibility with .net6.