A Randomized, Double-blind, Multi-regional Phase 3 Study of Cadonilimab Combined With Chemotherapy Versus Chemotherapy in Combination With or Without Nivolumab for the First-line Treatment of Participants With HER2-negative, Previously Untreated, Unresectable or Metastatic Gastric or Gastroesophageal Junction Adenocarcinoma | Arctuva