Replace `@error ...` by `error(...)` (or something else)?

It seems like `@error ...` does not stop execution anymore (it used to, didn't it 🤔). We still use it in ~6 places - should we change this to `error(...)`? Or is there even are more canonical way nowadays?

Search the repository for the roughly six uses of `@error` and inspect how execution behaves after each one. Check Julia's current error-handling guidance and existing project conventions before choosing an approach. Done means the intended behavior is consistent at every use site and covered by relevant tests, if present.

Written by the indexing model from the issue text.