Add support for mypy v0.910

• https://mypy-lang.blogspot.com/2021/06/mypy-0910-released.html
• https://mypy-lang.blogspot.com/2021/06/mypy-0900-released.html

With pyproject configuration support. Move option to the configuration

https://mypy.readthedocs.io/en/stable/config_file.html?highlight=pyproject#using-a-pyproject-toml-file

• Update to v0.910 in pyproject.toml and .pre-commit-config.yml

Install mypy attrs stubs to check types classes

Mypy v0.900 no longer install additional stubs by default Third-party Library Stubs in Stub Packages (Breaking Change)

attrs for duniterpy.documents.ws2p.heads

changed milestone to %1.0.0

added CI/CD Dev Env labels

May be we could replace attrs by Python standard library dataclass.

It will avoid to have to load the attrs stubs... and remove attrs dependency completely.

Sadly, dataclasses are only supported since Python 3.7. May be its too soon...

approved this merge request

mentioned in merge request !144 (merged)

mentioned in issue #88 (closed)

merged