Oklahoma closed the book on spring football in April, but that doesn’t mean the development process goes on ice throughout the summer.  The next few months are crucial as OU’s strength coaches get another chance to shape the team while the players work with each other to continue to build chemistry.  With no post-spring transfer portal window this season, every program across the country must look internally this summer to increase depth on the roster instead of to other rosters across the country.  Here are five Sooners who could raise Oklahoma’s ceiling this fall with a productive summer leading up to fall camp. DT Nigel Smith Oklahoma defensive lineman Nigel Smith tracks down John Mateer during one of the Sooners' spring practices.…