I wrote my own implementation of the hook I needed - shrimport.

It goes through all the files passed to it and checks them for relative imports that go beyond the package boundaries.

The tool also has useful arguments: -v / --verbose, -d / --dry-run, -i / --ignore and -R / --root-dir. You can read more about them in the tool help:

usage: main.py [-h] [-R ROOT_DIR] [-i IGNORED_PATHS] [-v] [-d] file_paths [file_paths ...]

positional arguments:
  file_paths            files to be processed

options:
  -h, --help            show this help message and exit
  -R ROOT_DIR, --root-dir ROOT_DIR
                        path to root directory (e.g., ./src)
  -i IGNORED_PATHS, --ignore IGNORED_PATHS
                        regex pattern to ignore file paths
  -v, --verbose         output extra information
  -d, --dry-run         run without changes

I hope I have helped you as much as I have helped myself.