Because reapportionment is primarily the duty and responsibility of the State through its legislature or other body, rather than of a federal court, Chapman v. Meier, 420 U.S. 1, 27, 95 S.Ct. 751, 766, 42 L.Ed.2d 766, the Court has tolerated somewhat greater flexibility in the fashioning of legislative remedies for violation of the one-person, one-vote rule than when a federal court prepares its