(In headline and paragraph 14, changes description of AI function to "tool"/"assistant" from "coach" ) By Waylon Cunningham Tacos with a heavy serving of AI, please. That's what Yum Brands' Taco Bell chain served up to Wall Street this week, the most recent effort by a major fast-food chain to promote newfangled labor-saving technology. Executives at Yum and Taco Bell showcased their "Byte by Yum" artificial intelligence-powered tools for restaurant managers, disclosing on Tuesday at a Yum