ZEPHYRHILLS, Fla. — For generations, Zephyrhills was the kind of Florida town people associated with retirement communities, bottled water, skydiving and a quiet downtown where life moved considerably slower than it did in Tampa. That version of Zephyrhills still exists. But increasingly, it is sharing space with something very different. New residents, housing developments, manufacturers and major investments are transforming this small Pasco County city into one of the east