Add more linting and other checks

[der-eismann]

To improve the quality of our package base, we need to introduce some opinionated checks and linters.
Ideas so far:

• Comparing the binary manifest to the stone.yaml/manifest.jsonc to ensure package was actually built
• At some point actually build changed packages in a PR and compare results
• YAML formatting in general
• Stuff inside the stone.yaml: Sorting of deps, trailing newlines etc

We implemented https://github.com/serpent-os/check-for-file-conflicts as a first step - pro: it's quick, relatively easy to read - con: it's TS/JS and we have nobody proficient in it. But it can do basically anything.