Regeneration of Cargo.nix files for testing depends on local paths

[kolloch]

and thus cargo test can not be used independently from the host.

Super annoying. Mostly due to the "opaque" package IDs containing local paths, I think, but I need to analyze further.

[kolloch]

So, I have enabled vendoring for most of the tests. Unfortunately, for tests dependending on git repositories with submodules, the vendoring code in ./tools.nix still does not work so there are still a couple of pregenerated files in the repo.

That said, ./run_tests.sh should work for everyone and I can easily rerun it on each pull request before merging.

[kolloch]

I am fine with the current state of affairs for now.

[kolloch]

Nah, I redecided since this is also an issue if you #102.