Nobody’s making a splash like Special Olympics swimmer Matthew Schuster, a 43-year-old testicular cancer survivor from Medford in Suffolk County.  “I’m the strongest kid on the block,” Schuster, who has Down syndrome, told The Post with a laugh. He will be racing in several aquatic events, such as the 100-meter individual medley, this weekend as Special Olympics New York comes to Massapequa’s Berner Middle School — a feel-good event for over 700  Empire State challengers making their way to the Town of Oyster Bay.  Matthew Schuster Schuster family photo Schuster (inset) has devoted his world to the games since he was just a little boy and is the de facto Mr. Olympia, having also competed in floor hockey, basketball, golf, softball and bocce. “It’s my whole life,” he said.…