Add a __version__ attribute to the package (PEP 396)

[jond01]

xil/__init__.py should contain a __version__ attribute.
It has to match the tool.poetry.version key in pyproject.toml (and ideally with the recent Git tag):

xil/pyproject.toml

Line 3 in 7813157

version = "0.1.0"

https://peps.python.org/pep-0396/

There are several ways to solve the single source of truth issues with Poetry.
Some options are:

• https://github.com/mtkennerly/poetry-dynamic-versioning

In some other build systems, this problem is solved:

• Hatch: https://hatch.pypa.io/latest/version/
• Flit: https://flit.pypa.io/en/stable/#usage
• PDM: https://pdm.fming.dev/latest/reference/pep621/#package-version
• https://packaging.python.org/en/latest/guides/single-sourcing-package-version/#single-sourcing-the-package-version

[jond01]

The selected solution with the Poetry plugin works.
However, it turned out to be complex. It will need to be revised after some time.

It will become much simpler once Poetry supports dynamic fields in the pyproject.toml file.
It might be resolved once python-poetry/roadmap#3 is completed (currently in the making: python-poetry/poetry-core#567).