feat: adding source based coverage using cargo-llvm-cov

[jrmncos]

Using cargo-llvm-coverage to generate source based coverage. The library is wrapper of the compiler flag -C instrument-coverage more details here

The command cargo llvm-cov --all-features --workspace --html --output-dir coverage was tested locally and it generated an html file with the coverage.

I used Github page to publish the .html file, but Codecov can be used too. I need to verify is there are free plan options.

Any change or suggest will be welcome!

#684