By ALYSON WARD The last of the Cliburn competitors will leave town today. For the three weeks they’ve been in Fort Worth, the 29 phenomenally talented young musicians at the Van Cliburn International Piano Competition have vied — and practiced and prayed and sweated and longed — for the exposure and recognition that could jump-start their emerging careers.After three rounds of high-stakes, high-pressure competition, a handful of these young pianists are leaving with prizes, professional management and guaranteed concert tours.