[TASK] Improve `IntoJobDefinition` unimplemented message

[Serial-ATA]

Overview

The unimplemented message for IntoJobDefinition isn't very helpful:

no method named `into_job_definition` found for fn item `fn(Context<OrbitContext>, ...) -> ... {modify_rollup_metadata}` in the current scope
the full type name has been written to ...

At least give some hint as to what's wrong.