MyPy wants some extra love nowadays, and Black needs special handling as
well. The latter is only available as beta-release, and Poetry only has "allow
pre-release versions" as global flag, installing way too many beta packages
for my taste.
This does introduce some not-so-nice things, like having to annotate each
`__init__` function with `-> None`. However, the benefits of having static
type checking in a complex bit of software like BAT outweigh the downsides.
