NEW YORK — Billionaire investors Steven Cohen and Ray Dalio have joined the cryptocurrency craze by putting cash to work and saying at a conference this week that bitcoin and other digital currencies are an interesting way to diversify their holdings. Dalio, who founded the world’s largest hedge fund, Bridgewater Associates, told attendees at the SALT conference in New York on Wednesday, “I have more crypto than gold.” Cohen, who runs Point72 Asset Management, said earlier this week at the conference that he hopes not to miss out on opportunities presented by the digital currencies.