WASHINGTON — The U.S. economy ended 2021 by expanding at a healthy 6.9% annual pace from October through December, the government reported Wednesday, a slight downgrade from its previous estimates. For all of 2021, the nation’s gross domestic product — its total output of goods and services — jumped by 5.7%, the fastest calendar-year growth since a 7.2% surge in 1984 in the aftermath of a brutal recession. Previously, the government estimated growth in last year’s fourth quarter was 7%.