The long-slowing rate of population growth in the U.S. has ebbed to its lowest level since at least the start of the 20th century, according to federal figures released Tuesday. Between July 2019 and July 2020 — a stretch that includes the early months of the coronavirus crisis — the American population climbed by just 0.35%, according to Census Bureau estimates. William Frey, a demographer at the at the Brookings Institution, said the pandemic’s deadly effects have compounded with pandemic-era immigration restrictions, stifling population growth. In the previous round of annual figures, the p…