Fixes stack overflow due to large test files

[waynebowie99]

I was running into issues where one of our larger projects that has a massive test file was causing tests to not be able to run. Looking into the logs, it all seemed to stem from a stack overflow error due to the recursive nature of the post process method for XUnit. I was able to change it to not be a recursive function and everything works perfectly for me and loads fairly quick

I also had to change the proj_root to come from the solution instead of the cs project. This might break some behavior. Without this change, everything locked up and never loaded any tests

[Issafalcon]

Thanks @waynebowie99 . I'll be looking into this as soon as I can. However, one thing I really need to do with this plugin is implement something like GustavEikaas/easy-dotnet.nvim#74. I think it will solve a lot of outstanding issues with this adapter, and hopefully performance issues too.

I'll keep your PR on the back-burner though, as it may help once the widespread changes mentioned, have been made.