maintenance chores
The overall repo is clean, well done
I was able to run all tests, and this MR is just providing few cleaning steps.
Next things I would suggest would be:
- use auto format tools. clang-format-12 for C++ and black for python. It would be my pleasure to help on this point
- I'm not sure how relevant is the current split in C++/python in the file hierarchy is. But it works, so no problem for now.