Add Python 3.13 support

[jank324]

Description

Adds Python 3.13 to the versions tested and upgrades all other test and format check runs (different OSs, flake8, black etc.) to run on 3.13.

Motivation and Context

Python 3.13 was released two days ago. Closes #271.

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist

• I have updated the changelog accordingly (required).
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have reformatted the code and checked that formatting passes (required).
• I have have fixed all issues found by flake8 (required).
• I have ensured that all pytest tests pass (required).
• I have run pytest on a machine with a CUDA GPU and made sure all tests pass (required).
• I have checked that the documentation builds (required).

Note: We are using a maximum length of 88 characters per line.

[jank324]

We are keeping this in draft for now because it seems at least one dependency isn't compatible with Python 3.13 yet.

[jank324]

Specifically the issue is PyTorch, and 3.13 support there is only expected for v2.6 (pytorch/pytorch#130249).

[jank324]

PyTorch 2.6 should be released tomorrow. I just ran a local test with the RC and everything seems to work fine.