integrate a code coverage tool

[nclack]

building with llvm

There's a way to do it via a visual studio toolchain, but it might be better to just use ninja, choco install llvm and specify clang and clang++ as the C/CXX compilers for cmake. Need to add compiler flags for instrumenting coverage and may need to link the profiler lib.

references:

https://andreasfertig.blog/2020/12/cpp-insights-code-coverage-on-windows/
https://github.com/andreasfertig/cppinsights/blob/main/.github/workflows/ci.yml

https://marco-c.github.io/2018/01/09/code-coverage-with-clang-on-windows.html