This is a follow-up of #1147 to greatly simplify and speed-up the whole build CI pipeline.

Overview of changes

• building a (redistributable!) wheel for a platform is now as simple as pip install cibuildwheel && cibuildwheel. The resulting wheel will be available in the wheelhouse subdirectory. Some notes about this:
  • by default, it builds wheels for all Python versions supported by NMODL (currently 3.8-3.12); for quick testing and development, set the env variable CIBW_BUILD to something like cp311* (for Python 3.11) to only build a wheel for a specific Python version
  • the wheel built is native to the platform (on Linux, or if specifying --platform linux in the above, Docker is needed; if you have podman instead, set CIBW_CONTAINER_ENGINE=podman)
  • on MacOS, you need the installer from python.org (the Homebrew-installed one won't cut it)
  • on MacOS, we also run some tests once the wheel is built
  • on Linux, we only run tests in the CI (why? Because the manylinux Docker image used for building the container does not come with the Python shared library); if you want to test the built wheel locally on Linux, run bash packaging/test_wheel.bash $(command -v python3) WHEEL, where WHEEL is the wheel you just built
• as a result of all of the above, removed packaging/build_wheels.bash
• simplified CI to use cibuildwheel everywhere. This comes with a big reduction in the CI build time (see for instance old vs. new, 16 minutes per Python version vs. 7 minutes). By default we build wheels for all Python versions, which is probably not optimal, and I don't have strong opinions on this, so whatever the popular vote decides is fine by me (build all/build specific version/build oldest/build newest/build oldest and newest)
• so far ARM64 builds work without issues, it's just a matter of setting up the proper CI pipeline (Azure doesn't have ARM64 MacOS runners, and GitHub doesn't have ARM64 Linux runners; for the former we can use GitHub, and for the latter we can use CircleCI), which, following some internal discussions, I am leaving out of this PR
• update docs

What works

• manylinux on x86_64 and ARM
• MacOS on x86_64 and ARM

What needs work

• after a bunch of Windows-specific fixes, jinja on Windows still has some issues with discovery of files, see https://github.com/BlueBrain/nmodl/actions/runs/7915828954/job/21608472715 EDIT: leave Windows support for later
• build time on Linux per Python version can take a while (5 minutes) on x86_64, and, due to the need for QEMU, is even longer on aarch64. If we only want x86_64 builds though, we should be fine (EDIT: added CircleCI to build aarch64 Linux since it has a native runner) EDIT: it now builds wheels much faster than master
• similar to the above, but with Python 3.8 on ARM on MacOS (however, there is a workaround for that one available) EDIT: ARM64 wheels are left for later
• testing of the wheels is not implemented yet (EDIT: done)
• we should update and/or build our own custom Docker images that have flex and bison to speed-up the building process; the current custom x86_64 latest image is 2 years old
• apparently on manylinux images, the libpython.so library is not available (as described here and in Fails to detect Python on cibuildwheel scikit-build/scikit-build-core#173) so some workarounds may be needed for testing the nmodl binary in a portable way. The Python module tests work like a charm though!