WYOMISSING, Pa. — A roller-coaster Pennsylvania campaign season careened toward a breathless finish Saturday as candidates raced to firehouses, diners, public parks, and an indoor rally, making a final push in some of the country’s most critical races. The scramble before Tuesday’s primary election was especially intense, and potentially decisive, in the Republican Senate race, where three candidates are running neck-and-neck over shifting terrain. In a hugely expensive and nationally watched race, celebrity surgeon Mehmet Oz is clinging to what public polling has suggested is the narrowest of…