Global Sauna Market Size, Share & Demand Report By Sauna Type (Traditional Finnish Sauna, Infrared Sauna, Steam Sauna, Smoke Sauna, Bio/Hybrid Sauna), By Heat Source (Electric, Wood-Fired, Gas-Heated, Infrared), By End Use (Residential, Commercial, Institutional), By Distribution Channel (Direct Sales, Specialty Retailers, Online/D2C, Contractors), By Region & Segment Forecasts, 2025–2030