Remove duplicate packaging files; use Hatchling as packaging backend

[akx]

• Both setup.py and pyproject.toml is unnecessary and confusing. The files also had disparate contents (different licenses).
• requirements.txt is a legacy format (and wasn't read by anything in the repo).
• MANIFEST.in is not required with the Hatchling build backend.

[reneleonhardt]

Great to see that some projects consider modernizing their setup process, thank you Aarni!
I can't see any CI here, is the project really unusable in Python 3.13 and 3.14?

[akx]

is the project really unusable in Python 3.13 and 3.14?

No, it works fine on 3.13 if the Misaki dependency is fixed (my PR #25), likely 3.14 too (when it's out and binary wheels start appearing).

[reneleonhardt]

The classifiers in this PR explicitly don't contain 3.13 and 3.14, that's why I asked.

FYI onnxruntime doesn't build wheels for Python 3.14, making the installation fail there.

https://pythoninsider.blogspot.com/2025/07/python-314-release-candidate-1-is-go.html

Call to action (July 22, 2025)

We strongly encourage maintainers of third-party Python projects to prepare their projects for 3.14 during this phase, and where necessary publish Python 3.14 wheels on PyPI to be ready for the final release of 3.14.0, and to help other projects do their own testing. Any binary wheels built against Python 3.14.0rc1 will work with future versions of Python 3.14.