As far as I can see Zonemaster::Backend::DB::sub store_results() is not used anywhere besides in t/lifecycle.tand could be removed.
https://github.com/zonemaster/zonemaster-backend/blob/develop/lib/Zonemaster/Backend/DB.pm#L431-L449
Furthermore, the database definitions of table "test_results" include a field "results" which is not used anymore, as far as I can see.