(Reuters) -Nvidia far exceeded expectations with its quarterly revenue forecast on Wednesday as an artificial-intelligence boom fueled demand for its chips and said it would buy back $25 billion in stock, sending its shares soaring after hours. Nvidia's forecast beat expectations by billions of dollars, demonstrating that a boom in generative AI technologies that can read and write in human-like ways - and powered almost exclusively by Nvidia's chips - shows no signs of slowing down. Nvidia's ad