Two of Silicon Valley’s top tech firms are teaming up to change the payments landscape. On Thursday, the $91.5 billion fintech Stripe and the crypto venture firm Paradigm publicly announced their joint project Tempo, a so-called Layer-1 blockchain built around stablecoins, or cryptocurrencies typically pegged to the U.S. dollar. Layer-1 blockchains like Bitcoin or Ethereum are more demanding to build and operate than “Layer 2s,” which sit atop other blockchains. Tempo is among a new crop of laye...