There have been sibling rivalries in athletics before, but what Mia and Mariah Maxwell are doing goes considerably beyond rivalry. At the USATF U20 Championships in Eugene, Oregon, on Thursday, the twins from Atascocita High School in Humble, Texas, completed a double sweep of the women’s sprint events that will spark conversation for years. Mia won the 200m in 22.49 seconds with Mariah second in 22.86, following up a 1-2 finish in the 100m earl…