The wedding bells on "Cheers" helped ring in ratings bliss at NBC. The A.C. Nielsen Co. reported Tuesday that the season-ending episode of "Cheers" last Thursday, featuring the wedding of Woody and Kelly, was the most-watched TV program of the week, attracting viewers in about 20.6 million homes. That was the show's best performance since Feb. 28, 1991, the network said. NBC in turn won the week, averaging a 12.0 rating in prime time, compared to 11.6 for CBS, 11.4 for ABC and 7.3 for Fox. NBC also was victorious in the movie battle Sunday night, as Part 1 of "Cruel Doubt" drew a larger audience than Part 1 of CBS' "The Intruders" and ABC's telecast of "Look Who's Talking." Fox's season-ending episode of "Married . . . With Children" ran second at 9 p.m. that night.