Get working on python 3.12

[aragilar]

This gets scikits.odes building again, and moves away from numpy.distutils (see #130 and #166).

See the third commit comment (repeated below for more details):

This splits scikits.odes into 4 packages:

• scikits-odes-core: contains DaeBase and OdeBase which all other packages use. Uses setuptools as the build system.
• scikits-odes-daepack: contains the daepack fortran code plus f2py wrappers and associated python code. Uses mesonpy as the build system, as f2py really only supports mesonpy now.
• scikits-odes-sundials: contains the cython sundials wrappers. Uses setuptools as the build system, as meson does not align with how we're using cython.
• scikits-odes (using the correct normalised package name): contains the high-level wrapper code to switch between solvers. Also contains the compatibility code to allow old imports to work across the packages. Uses setuptools as the build backend.

Each package has its own directory, though currently there are symlinks to shared files, and the docs and API docs are for all packages (there hasn't been too much change there).

CI is also updated, with only scikits-odes-daepack failing due to conflicts between tox and meson. Tests haven't been moved, there is likely some cleanup to do, and to improve the code coverage of each of the packages.

[aragilar]

Merging this in preparation for doing an alpha release to confirm that everything is set up correctly.

[callegar]

Is a new release with this update expected soon?