The nights before Independence Day are loud in Cancún. Dog owners know the drill. Pets bolt under beds. Others shake, pant, or claw at doors the moment the first boom breaks over the neighborhood. This year, local animal-welfare advocates want the soundscape to change. They’ve asked authorities to discourage explosive pyrotechnics during the fiestas and to back that message with fines that could reach 30,000 pesos for those who light them anyway.…