MOORESVILLE, N.C. – Inside this former textile mill, a retro building built in 1892 with massive floor-to-ceiling windows and sturdy brick, Toyota has planted a future seed with the GR Cup. Once a hub for making cotton dye, the first floor has been turned into a factory that churned out spec sports cars for the past year as Toyota Racing Development prepares to launch its first single-make series. The inaugural season of the Toyota Gazoo Racing GR Cup will begin this weekend at Sonoma Raceway, the first of seven SRO-sanctioned events (each with two races) featuring a field of homologated GR86 production models that have been modified for racing with…