PHILADELPHIA — Travelers were required to wear masks inside Philadelphia’s main airport terminal Tuesday, but not after boarding many airplanes. They had to mask up to enter stores in the city, but not to ride the commuter rails. As local and federal COVID-19 safety requirements changed yet again this week, Philadelphia stood out for rules that often came into conflict inside the city’s most crowded locations. Philadelphia started the week by becoming the first large U.S. city to reinstate an indoor mask mandate, which some businesses are suing to block. Then late Monday, regional transit auth…