Vanguard Group, the world’s largest mutual fund manager, said it attracted a record $305 billion last year — an annual total that some firms need decades to reach. Vanguard’s take, which tops the firm’s previous record of $276.4 billion in 2015, includes $93 billion that went into exchange-traded funds, up from $76 billion the year before, spokesman John Woerth wrote in an e-mail.