An Open-Label, Single-arm Study to Evaluate the Pharmacokinetics (PK), Pharmacodynamics (PD), Safety, and Efficacy of Gefurulimab in Pediatric Patients (6 to < 18 Years of Age) With Generalized Myasthenia Gravis (gMG) Who Express Acetylcholine Receptor Antibodies (AChR+) | Arctuva