Add optional libraries

[freddieknets]

Description

This PR allows declaring C libraries using entry points, similarly to how include directories are declared.

In a package that depends on xobjects, you can register C source and library paths using the entry point xobjects.build_info. These paths will be added to the C include path and the library path when building kernels. For example, the following will allow to write #include <xcoll/path/to/some/header.h> in kernel sources, and allow to use functions from the library xcoll/lib/libFlukaIO.a:

In the pyproject.toml:

[project.entry-points.xobjects]
build_info = "xcoll._xobjects:get_build_info"

and in the file xcoll/_xobjects.py:

from ..general import _pkg_root
def get_build_info():
    return {
        "include_dirs": [_pkg_root.parent],
        "libraries": ["FlukaIO"],
        "library_dirs": [_pkg_root / "lib"],
    }

Checklist

Mandatory:

• I have added tests to cover my changes
• All the tests are passing, including my new ones
• I described my changes in this PR description

Optional:

• The code I wrote follows good style practices (see PEP 8 and PEP 20).
• I have updated the docs in relation to my changes, if applicable
• I have tested also GPU contexts