Use `classify-imports` instead of `isort` for import classification

[sisp]

I noticed that isort is used for classifying imports, which is something isort can do, but it's not isort's primary job. I wonder whether you've considered classify-imports which is a utility library that is also used in reorder-python-imports, which is an an alternative to isort that performs static import analysis. It might be a lighter and more tailored dependency to solve that problem. Just an idea. 😇

[aguschin]

Hi @sisp! Thanks for a suggestion! @mike0sv was selecting isort for the purpose, and I'm not sure if he was considering anything else. We'll keep this in mind in case we'll need a better alternative.