Python 3.9 is EOL

[m0uss3]

python 3.9 reached eol as of 2025-10-31. python 3.10 is still supported but will too be retired later this year. python 3.10 brings support for union types which are used in the codebase (one here). 3.9 does not receive security updates, so maybe it's time to start thinking about removing support for it in trackma?

[z411]

Trackma runs fine on Python 3.9 and a few LTS distros still package it (with backported security patches) so I've temporarily removed the mentioned union type hint so it works for now. That said, I agree with the rationale and I would also like to migrate the code base to using proper type hints so I'd like to drop it soon as well. I've added a deprecation warning in case there's anyone using it still.