Find a way to run process-compose based tests on CI

[szg251]

process-compose-flake can spin up runtime deps, like cardano-devnet, postgres, etc., it would be nice to just use the same setup on the CI, but I couldn't figure out how.
Concretely:

• I need a cargo test derivation, which doesn't run checks right away (craneLib.cargoNextest does this), so I can pass it down to process-compose
• I need to wrap process compose into a derivations which runs the tests in checks