Python version support policy

As a developer I would like to clarify & discuss which python versions we should support.

Currently we _only_ support 3.11 (and even specify a patch version)

## Options

- What we currently do: just one version, but that's not great for sharing with other groups and limits the benefit that we get from packaging genie_python
- "Industry standard" for scientific python is [SPEC00](https://scientific-python.org/specs/spec-0000/) which typically covers 3 recent python versions
- If we need to support old(er) linux distributions e.g. RHEL, that may mean we need to support quite old python versions
- Something else.

## Acceptance criteria

Discuss options (e.g. in teams technical channel), and then actually make genie_python follow it & run at least the unit tests against those versions.

## Notes

Ask mantid, idaas etc what their python version support policy is for comparison