add mypy + classifiers

[chainyo]

This PR:

• Add classifiers to the pyproject.toml, especially the License one (useful for badges usage)
• Add mypy to quality dependencies along with its command: hatch run quality:typecheck Either remove py.typed or add mypy support #16

[alvarobartt]

Thanks a lot @chainyo! This is really useful, is it ready to merge? 🤗

[chainyo]

@alvarobartt ready to go

I might add an update on the GitHub ci workflow in the next PR. Also to add mypy to the ci workflow.