`ActiveRecord::Relation.exists?` yields a SQL EXISTS query, while `present?` is a method of Enumerable, which needs the actual result array to be queried.
- rename `dossiers_id_with_notifications` to `followed_dossiers_with_notifications`,
- rename `notifications_per_procedure` to `procedures_with_notifications`,
- return an ActiveRecord::Relation instead of the result of the query, so that the call place can compose it,
- `merge` with the wanted Dossier scope in the call places, don’t bother passing it as a parameter,
- use the “state” (now “scope”) parameter as a scope method that can be just applied on `Dossier`.
