Replace Boost.Python with pybind11

[CalaW]

This PR replaces Boost.Python with pybind11, which has become the de facto standard for Python bindings in C++.

Key improvements:

• Simplified binding code, thanks to pybind11’s automatic handling of standard containers.
• Easier build process, as pybind11 is a lightweight, header-only library.
• Additionally, this PR includes fixes for existing CI errors. I'm happy to split those into a separate PR if preferred.

Note: This is still a draft. Documentation updates are pending. Please review the current changes and share your feedback. Once everyone is on board, I’ll proceed with updating the docs.

This should resolve #164.

[CalaW]

Hi @aewallin @vespakoen, just following up on this PR. If either of you happens to have some spare time, would you mind giving it a look or testing it out? I’d be happy to make any necessary changes. Thanks in advance!