Add support for python 3.14

[liamlundy]

I can't install the latest luigi because its only support up to 3.13. What needs to happen to enable it for 3.14? I'm happy to create a PR if there is a process to follow.

I'm assuming at the bare minimum it needs the following tasks:

• Modify pyproject.toml
• Add 3.14 to unit test matrix

[hirosassa]

@liamlundy I think it's good to go! There may be some dependencies that don't support the latest version of Python.