SAN FRANCISCO, April 30 : Memory chip maker Sandisk on Thursday reported soaring revenue and profit while predicting another rosy quarter, adding it has signed long-term contracts worth at least $42 billion to help it counter any extreme price cycles. It also said it would embark on a $6 billion buyback. Sandisk has become one of the later beneficiaries of the artificial intelligence boom, with its main product - NAND storage memory - now in high demand as AI systems have started to work with