Boxboard Packaging Market Size & Forecasts 2026-2035, By Segments (Thickness, Materials Type, Product Type, End Use), Growth Opportunities, Innovation Landscape, Regulatory Shifts, Strategic Regional Insights (U.S., Japan, China, South Korea, UK, Germany, France), and Competitive Dynamics (International Paper, WestRock, Smurfit Kappa, Stora Enso, DS Smith)