A Phase III, 12-week, Prospective, Randomized, Double-blind, Placebo-controlled, Parallel-group, Multi-center Study to Determine the Efficacy, Safety, and Tolerability of a Dose of 15 mg Bid of Evenamide as add-on in Patients With Documented Treatment-resistant Schizophrenia, Which is Not Adequately Controlled by a Stable Therapeutic Dose of the Patient's Current Antipsychotic Medication(s) | Arctuva