Add functionality to get python objects created during string cmd

[isteinbrecher]

This PR adds the functionality to get python objects created during string cmd. One can now execute a string command with the wrapper cmd_return and this function returns the created geometry objects.

[isteinbrecher]

@danielwolff1 I think this should be pretty much exactly what we talked about a while ago. I needed this and I think this PR should provide a general working implementation, I am looking forward to your review.

I decided to only wrap string commands, as "pure" python commands usually return the relevant created geometry. If we also want to allow a similar functionality there, I would do that in a follow up PR.

[danielwolff1]

Thanks a lot for this great addition. This is much more advanced than the solution that I came up with since it tracks all geometric entities, I really love it and can't wait to see it merged soon! 😊

I just had three small questions, but we can also discuss in person after your vacation 😄

[isteinbrecher]

@danielwolff1 this should add the changes we talked about offline. Now we have two functions with unique signatures, that should ease their usage and avoid confusion.

[danielwolff1]

Thanks a lot for adapting the implementation, this looks good from my point of view and we can merge this right now, I can't wait to see this functionality in cubitpy! 🥳