Who's minding the store? In the not-too-distant future it could be cameras and sensors that can tell almost instantly when bruised bananas need to be swapped for fresh ones and more cash registers need to open before lines get too long. Walmart, which faces fierce competition from Amazon and other online retailers, is experimenting with digitizing its physical stores to manage them more efficiently, keep costs under control and make the shopping experience more pleasant. On Thursday, the retail giant will open its Intelligent Retail Lab inside a 50,000-square-foot Neighborhood Market grocery store on Long Island.