Investors are questioning the artificial intelligence trade that sent power stocks soaring last year, as the company viewed as best positioned to strike a data center deal still has not signed an agreement. Vistra Corp. was a darling of the S & P 500 in 2024, more than tripling in value to become one of the best performing stocks as investors expected the company’s nuclear and gas assets to benefit from the growing power demand of data centers. But Vistra’s stock fell more than 11% this…