startOfDecade
import { startOfDecade } from "https://esm.sh/v135/date-fns@3.6.0/index.d.mts";@example
// The start of a decade for 21 October 2015 00:00:00:
const result = startOfDecade(new Date(2015, 9, 21, 00, 00, 00))
//=> Jan 01 2010 00:00:00
function startOfDecade<DateType extends Date>(date: DateType | number | string): DateType;