This is an education in extravagance. The Syosset Central School District, which serves an enclave of gated communities, ritzy eateries and children's boutiques like "Spoiled Rotten," takes the crown in employee compensation. The school superintendent, Carole Hankin -- who oversees 6,687 kids in 10 schools -- is the highest-paid in the state with $506,322 in total compensation. She collects a $386,868 salary, $67,454 in fringe benefits and $52,000 in retirement funds and expenses including use of a "late model car," plus gas. By contrast, New York City Chancellor Cathie Black, in charge of 1.1 million students and