Allow Python versions higher than 3.9

[norpadon]

It is currently impossible to add equinox to a modern Python project using Poetry, because the current pyproject.toml says that it only supports Python 3.9

This PR fixes this

[patrick-kidger]

I think this is correct as-written. ~=3.9 means that anything in the 3.x series above 3.9 is acceptable.

See the PyPA documentation here: https://packaging.python.org/en/latest/specifications/version-specifiers/#compatible-release

For some reason Poetry appears to use a nonstandard interpretation of this: https://python-poetry.org/docs/dependency-specification/#tilde-requirements

If my understanding is correct then I believe this is a bug in Poetry, and it should be reported there. (A quick search on their GitHub looks like this might have come up before: python-poetry/poetry#380)

(These days I would strongly recommend using uv instead. Similar to poetry, fewer bugs, much faster.)

[norpadon]

Oh, I think you are correct. The problem was on my (importing) side: I was specifying requirements as

python = ">=3.12"

But it theoretically includes python = "4.0", which is technically not compatible with python = "~=3.9".
So I fixed the problem on my side by changing python version requirements to "~=3.12"

This is indeed a technically correct behaviour, but I am not sure whether being "technically correct" is worth it, given that the likelihood of python4.x being released is negligibly small. Almost every other python package has ">=" in python version requirements, and equinox is the first package I had this issue with. Maybe switching to ">=3.9" on the equinox side is simply better for the user experience.

[patrick-kidger]

Agreed. Whilst Poetry is definitely wrong here, it's a pragmatic choice for us to allow compatibility in this way. Merged! :)