WASHINGTON — Tens of thousands of federal inmates serving time for drug crimes may be eligible for early release under a cost-cutting proposal adopted Friday that would dramatically reduce the nation’s prison population over time. The U.S. Sentencing Commission, which earlier this year voted to substantially lower recommended sentences for drug-dealing felons, voted unanimously to retroactively apply that change to prisoners now behind bars. More than 46,000 inmates, including many who have already …