MIAMI — A U.S. federal narcotics agent known for his expensive tastes and high-profile drug seizures has been implicated in a multimillion-dollar money-laundering conspiracy that involved the very cartel criminals he was charged with fighting in Colombia. A once standout Drug Enforcement Administration agent, Jose Irizarry is accused of conspiring with a longtime DEA informant to launder more than $7 million in illicit drug proceeds, sometimes using an underground network known as the black-market peso exchange, according to five current and former law enforcement officials. The officials described the case as one of the biggest black eyes in the history of the DEA, an agency that has seen repeated scandals in recent years, and one they fear could have compromised undercover operations in the U.S.