Mercedes Márquez, left, is departing as L.A. Mayor Karen Bass’ top housing and homelessness official, to be replaced by Lourdes Castro Ramírez. Mayor Karen Bass’ homelessness czar, Mercedes Márquez, will leave her high-profile post next month, with state housing official Lourdes Castro Ramírez set to succeed her, the mayor’s office announced Monday. Castro Ramírez will start her tenure as the …