Darwin: inconsistencies between CI and Runtime

[shivaraj-bh]

CI uses nix flake check, which calls the process-compose app wrapped inside pkgs.runCommand. The apps that run inside runCommand gets a few packages by default, for example readlink from coreutils. This behaviour could make the tests pass in CI but fail on runtime (when ran using nix run), if the service doesn’t pass those packages in its environment.

For more detailed analysis, see: https://github.com/juspay/services-flake/pull/164#issuecomment-2053876700