LOS ANGELES — One of the deadliest accidents in recent U.S. maritime history was the fault of owners of a Southern California dive boat whose lack of oversight resulted in a fire that swept through the vessel and killed 34 people in their bunks below deck, federal safety officials ruled Tuesday.The National Transportation Safety Board said the Conception’s captain failed to post a roving night watchman aboard the vessel, which allowed the fire to quickly spread and trap the 33 passengers and one crew member. The NTSB also …