build: added cloc Makefile target to easily count loc

[ErikBjare]

Just a tiny cloc make target to easily count loc in the project. I found it useful to understand where complexity hides.

[sweep-ai]

Apply Sweep Rules to your PR?

• Apply: Ensure all new functions and classes have very clear, concise and up-to-date docstrings. Take gpt_engineer/ai.py as a good example.