ops: poetrify

[kerberizer]

• switch from setup.py to pyproject.toml (info)
• use poetry for dependency management and project packaging
• reogragnize accordingly the development and testing workflows
• drop the unmaintained environment.yml and requirements.txt files
• other ops improvements

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[kerberizer]

There's still work to better integrate tox with poetry.

[kerberizer]

I'm now considering replacing Poetry with Hatch. Hatch is more standards compliant and is maintained by PyPA themselves. Poetry does have its own strengths, but one specific benefit of Hatch over it is that it can replace tox completely, e.g., by supporting multiple virtual environments vs a single one in the case of Poetry.

Edit: Still no editable dependencies might be a dealbreaker for Hatch though: pypa/hatch#588