New York will build the nation's first prison exclusively for drug addicts and alcoholics as part of an $886.6-million plan to put 7,100 more inmates behind bars, Gov. Mario M. Cuomo and legislative leaders said. The deal calls for construction of six new medium-security prisons scattered across Upstate New York. It will also create seven "annexes" built onto existing prisons that would provide drug treatment and counseling for inmates within two years of parole eligibility. The new drug prison, to be built at a cost of $65 million near the U.S. Army Depot in Romulus, Seneca County, will offer comprehensive treatment.