Apple, aiming to boost sluggish computer sales, is preparing to overhaul its entire Mac line with a new family of in-house processors designed to highlight artificial intelligence. The company, which released its first Macs with M3 chips five months ago, is already nearing production of the next generation — the M4 processor — according to people with knowledge of the matter. The new chip will come in at least three main varieties, and Apple is looking to update every Mac model with it, said the people, who asked not to be identified because the plans haven’t been announced. The new Macs are underway at a critical time. After peaking in 2022, Mac sales fell 27 percent in the last fiscal year, which ended in September. In the holiday period, revenue from the computer line was flat. Apple attempted to breathe new life into the Mac business with an M3-focused launch event last October, but those chips didn’t bring major performance improvements over the M2 from the prior year. Apple also is playing catch-up in AI, …