LAS VEGAS — The Knicks Summer League roster is obscure, the product of going through the last two drafts without a first-round pick. But one player who has a chance to crack Tom Thibodeau’s rotation is Isaiah Roby. The 25-year-old is among the most seasoned veterans across the Vegas Summer League, having logged 151 NBA games (mostly with the OKC Thunder) after getting drafted in the second round of 2019. The Knicks signed Roby toward the end of last season, giving him $400,000 up front with the hope of bringing him into the 2023 training camp. Then a potential rotation spot opened up last week when Obi Toppin, the reserve power forward, was traded to the Pacers in what amounted to a salary dump.