BEIJING — Migrant workers in central China are fleeing one of the world’s largest iPhone factories amid a coronavirus outbreak in the surrounding city of Zhengzhou, leading local officials to hastily draw up plans to isolate them once they return to their hometowns. Zhengzhou, capital of Henan Province, reported 167 locally transmitted Covid-19 cases in the seven days to Oct. 29, up from 97 infections in the prior seven-day period. Apple supplier Foxconn, based in Taiwan, currently has about 200,000 workers at its Zhengzhou complex and has not disclosed the number of infected workers, but said on Sunday that it…