pre-commit: Upgrade black v25.1.0 and isort v6.0.0

[cclauss]

% pre-commit autoupdate

[https://github.com/pre-commit/pre-commit-hooks] already up to date!
[https://github.com/psf/black] updating 24.10.0 -> 25.1.0
[https://github.com/pycqa/isort] updating 5.13.2 -> 6.0.0
[https://github.com/pycqa/flake8.git] already up to date!

% pre-commit run --all-files

https://github.com/psf/black/blob/main/CHANGES.md#2510

This release introduces the new 2025 stable style

https://github.com/pycqa/isort/releases

Python 3.13 support...