SAN DIEGO — Despite growing up poor in the stronghold city of the Sinaloa Cartel, Juan Manuel Álvarez Inzunza overcame a difficult childhood and earned a law degree, even leaving his hometown for a time to avoid the drug violence that hung over the region. But roughly a decade ago, a cartel figure entered Álvarez Inzunza’s private civil law practice in Mexico. “The wrong client came in, and he listened to them,” his attorney said Friday during a sentencing hearing. That launched Álvarez Inzunza’s own criminal career as a high-ranking money launderer who cleaned millions of dollars in drug proc…