WASHINGTON — The U.S. charged seven hackers linked to the Iranian government with executing large-scale coordinated cyberattacks on dozens of banks as well as a small dam outside New York City — intrusions that law enforcement officials said reached into America’s infrastructure, disrupted the nation’s financial system and cost tens of millions. Indictments announced Thursday by the Justice Department show a determination by overseas hackers to cripple vital American interests, officials said, and marked the first time the FBI attributed a breach of a U.S.