Change aware tests

Currently we run all tests for each PR irrespective of which files have changed. It would be nice if we can test just what was modified based on changed files.

Each blueprint test knows which root module it actuates so an initial version of this could do a git diff and understand if changed files affect current module and t.Skip if is not changed. However we likely need some rules like any changes to a module/submodule should override this heuristic and run all tests regardless.

Further if we can become config aware, i.e example foo which is the test root module uses module bar, we could restrict the tests that way too.