In South Korea, where a mountainous landscape makes building huge projects an incredible undertaking, the world's leading maker of high-bandwidth computer memory is investing $720 billion on what it says will be the largest network of memory factories in the world.SK Hynix, whose market cap has jumped more than fivefold in the past year and now tops $1 trillion, is making a big bet that extreme demand from artificial intelligence is here to stay. Soaring prices exacerbated by capacity constraint...