install build-essential to compile dependencies and use multi-stage build (#2582)

- Install build-essential to avoid build issues like #2568 when dependencies don't have prebuilt wheels available
- Use multi-stage build instead of trying to purge packages and cache from the image
  Copying `/root/.local/` installs only black's built Python dependencies (< 20 MB).
  So the image is barely larger than python:3-slim base image