Less than two weeks before the digital artist Beeple made headlines for selling a $69.3 million JPG, the young 3D art collective RTFKT teamed up with 18-year-old artist Fewocious to design a collection of digital sneakers and charms. In just seven minutes, they generated $3.1 million, according to RTFKT’s Instagram. NFTs, or nonfungible tokens—unique digital…