Feat/cleanup

[Oisin-M]

Description

Some small cleanups

• deletes unused envs
• simplifies Makefile
• updates pyproject to have python 3.14 classifier, and updates licence spec as per https://peps.python.org/pep-0639
• updates hpc ci config to use pyproject deps instead of nonexistent downstream-ci-requirements.txt

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[sandorkertesz]

@Oisin-M, thanks for this clean-up, it all looks fine. However, the conda based development instructions should also be updated indocs/source/development/conda.rst.

[Oisin-M]

@Oisin-M, thanks for this clean-up, it all looks fine. However, the conda based development instructions should also be updated indocs/source/development/conda.rst.

Added now. We might at some point consider just have a single development instruction since the conda and venv setups are more or less the same now, but can be done later.