add recipe for clippy to justfile

[imabdulbasit]

This PR adds a clippy recipe to the Justfile.
Usage: just clippy.

[sveitser]

This is fine but I think we shouldn't duplicate the clippy command we have in flake.nix yet another time. It's already duplicated in the CI job. We can replace the pre-commit hook inside flake.nix with just clippy in addition to the change in this PR.

If you're using the nix dev env you can also run pre-commit run cargo-clippy --all-files to run the pre-commit hook. Similarly for the other hooks.