`--noNimblePath` should unconditionally be set for projects with lock files
If a project has a lock file, plain `nim` and tooling should be prevented from ever looking into the nimble folder, so as to avoid that random code from the global nimble cache infects the project.

The current strategy with a conditional `when fileExists("nimble.paths"):` breaks before `nimble setup` has been run, because `nimble.paths` does not exist on a freshly cloned repository.
