By Carmen Reinicke and Rainier Harris, Bloomberg Micron Technology Inc.’s earnings report on Wednesday afternoon is shaping up to be one of the most important in months as investors find themselves suddenly on edge over the sustainability of the AI rally. The memory-chip maker’s shares have soared about 270% this year amid insatiable demand from data-center developers. The gain has made Micron the biggest point contributor by far to the roughly 8% advance in the S&P 500, whose leader board is dominated by other memory and storage companies including Sandisk Corp., Western Digital Corp. and Seagate Technology Holdings Plc. But...