Explain why the tests are all individual applications in ARCHITECTURE.md

[kammce]

First, we need to create an architecture.md file, but the purpose of why I split up the tests are:

1. Isolate tests from each other
2. Better integrate with ctest which is designed with the idea that tests are separate applications

The applications contain a run_test function because putting the tests in the main function, results in UB when built using Relase mode and LTO .

We cannot use test suites as they This does not work on Windows for some reason, with LLVM.