More than 40 African startups from a handful of countries have gone through YC over the past decade. Zambia joins that list today, and its entrant, Union54, is a worthy first entry. Union54 (54 is a nod to the number of African countries) is a fintech company founded by Perseus Mlambo and Alessandra Martini. The startup claims to be Africa’s first card-issuing API and only just launched this year. But to paint the picture, Union54 didn’t come out of thin air; it is a project from the couple’s earlier startup…