code formatting

[Podidiving]

Hi 👋 I've reformatted code a little bit to make it prettier.

1. black formatting. Flag -l=100 is used
2. isort formatting
3. check code with flake8. Flag --max-line-length=100 is used

For convenience, I've added Makefile with format-code and check-code targets

Also, I've renamed test_ai_function.py to test_ai_functions.py. I believe it was a typo

Hope, you'll find it useful!