A Study to Evaluate the Dose-exposure, Safety, and Exploratory Efficacy of Nerandomilast in Children and Adolescents From 2 Years to Less Than 18 Years of Age With Fibrosing Interstitial Lung Disease (Part A: Double-blind, Placebo-controlled in Children From 6 to Less Than 18 Years of Age and Open-label Active Treatment in Children From 2 to Less Than 6 Years of Age), Followed by an Open-label Phase With Active Treatment (Part B) | Arctuva