Mortgage rates have declined for the first time since the outbreak of conflict in Iran, providing some relief to the U.S. housing market as the spring homebuying season begins. The average rate on a 30-year fixed mortgage slipped to 6.37% on Thursday, down from 6.46% the week before. At this time last year, the rate was 6.62%. Rising borrowing costs and higher energy prices, driven in part by tensions in the Middle East, have sparked concerns about the durability of the real estate market’s recent strength.