Close this pigpen! Filth-ridden Zuccotti Park is a breeding ground for bacterial infection loaded with potential health-code violations that pose a major risk to the public, an expert who inspected the area warned. “It’s like Walmart for rats,’’ Wayne Yon, an expert on city health regulations, said yesterday. “There’s a lack of sanitation, a lack of controls for hot and cold water,” Yon said. He saw at least 15 violations of the city’s health code -- the type that would easily shut down a food establishment.