Investigate what version of python we actually require

[helen-fairclough]

Rhino/Grasshopper is fixed to running on Python 3.9. This will be updated to 3.13 when Rhino 9 comes out (likely 2027) but currently that means you cant run layopt in Rhino/Grasshopper without using the beta version.

If there are actually 3.13 features we need then that's ok, people will have to wait/use the beta version, but if we don't actually need it then it would be good to run tests on 3.9 and change the published requirements.

[ns-rse]

We can easily drop the minimum version, I don't think there is anything particular to Python 3.13 that we use but I
opted for a minium of Python >=3.12 as 3.10 reaches end of life 2026-10 and 3.9 reached end of life
2025-10 and its good practice to stay on top of version updates.

This will require modifying...

• pyproject.toml to update...
  • requires-python = ">=3.12" to ">=3.9"
  • classifiers where we have "Programming Language :: Python :: 3.12", to include the other earlier versions 3.9, 3.10 and 3.11
• .github/workflows.tests.yaml
  • update the python-version: ["3.12", "3.13", "3.14"] to include 3.9, 3.10 and 3.11

I don't think we need to explicitly change pypi.yaml it uses ${{ matrix.python-version }} to set up uv but since
we are making plain wheels we only build one and upload it to PyPI.

[ns-rse]

Have started work on this, not quite as straight-forward as I'd imagined since we also have pinned versions of pytest
and pytest-cov and these require newer versions of Python since they don't support those that are end-of-life.

Removing the pins has allowed installation though.

However, we have made wide use of modern syntax for Python's type hints and since version 3.10 the | (or) operator has
been supported but isn't under 3.9 where you are expected to from typing import Union and use Union[str, Path] if
there is more than one type.

I'm wary of moving our code backwards just to support a version which has been end-of-life for eight months already
especially as developers of Rhino/Grasshopper are aware and working on moving to Python 3.13.

Perhaps we could add to our documentation advice on using the Beta version? That may come with some risks of instability
though.

(These sorts of dependencies are what make packaging hell!)