MEXICO CITY — Mexican President Claudia Sheinbaum on Tuesday announced a new security strategy for the violent state of Michoacan, where people have taken to the streets to protest the most recent mayoral assassination, the seventh of the past three years. The lethal attack Saturday against Uruapan Mayor Carlos Alberto Manzo, who had gained popularity for his stance against cartels and criminal groups, fueled criticism of the Sheinbaum administration’s security policies and Mexicans’