LAS VEGAS — He arrived as a rookie but has shown the poise of a veteran. That makes it easy to see what the Miami Heat saw in Zyon Pullin as a combination of polish and potential. After four seasons at California-Riverside and then this past season at Florida, the 23-year-old point guard has displayed the type of savvy with the Heat’s summer roster that one might expect from a player with 142 games of collegiate experience. Where many teams shy from players with extended college resumes, as if a 23 year old somehow would age out, the Heat have thrived with such experience, from the 136 college games of Josh Richardson, the 147 of Duncan Robinson or the 134 of Jaime Jaquez Jr. Where some teams struggle at summer league while experimenting with rookie point guards, the Heat largely have shown balance in Pullin’s minutes, as he probes defenses with patience beyond his years. “I would say that’s one of the biggest things that we like about him is his poise, he plays under control and his ability to make plays for others,” said Heat assistant Dan Bisaccio, who is guiding the team’s summer roster.