ANCHORAGE, Alaska — Winter is off to a late start in parts of the nation’s largest — and usually coldest — state. Months of higher-than-normal temperatures in parts of rural Alaska have opened dangerous gaps in frozen rivers that residents use to travel from village to village and to hunting grounds since there are no roads. One troublesome ice highway is the half-mile-wide Kuskokwim River, where a man died New Year’s Eve after he and five family members — traveling on a snowmobile and sled — fell into a gaping hole.