Some of the most prominent players in the digital-assets industry cut their teeth at the same place: Fidelity Investments. A storied mutual-fund powerhouse, Fidelity is a cornerstone of the traditional financial system that the founders of bitcoin and other cryptocurrencies intended to disrupt. Yet the 77-year-old company became a bitcoin pioneer in 2014, launched its crypto business unit four years later, and built a deep talent pipeline for the industry along the way.