Use ufmt for code formatting and import sorting

[Balandat]

ufmt (https://ufmt.omnilib.dev/en/stable/) is a tool that combines code formatting (via black) and sorting (via usort). It's been working great for us for other projects. This PR enables the ufmt style in GitHub actions and pre-commit.

µfmt formats files in-memory, first with µsort and then with black, before writing any changes back to disk. This enables a combined, atomic step in CI/CD workflows for checking or formatting files, without any chance of conflict or intermediate changes between the import sorter and the code formatter.