Consider moving away from Pipenv

[c0c0n3]

Is your feature request related to a problem? Please describe.

It looks like these days Pipenv is falling out of favour among Python devs. A few reasons:

• Python moved to pyproject.toml as the blessed way of managing deps and packaging projects.
• Pipenv doesn't support pyproject.toml .
• It looks like the Pipenv project hasn't been very active recently.

We should probably consider introducing pyproject.toml too.

Describe the solution you'd like

Evaluate what our options are. See e.g.

• https://remastr.com/blog/pip-pipenv-poetry-comparison
• https://dev.to/frostming/a-review-pipenv-vs-poetry-vs-pdm-39b4

Then make a plan to migrate our Pipfile-based setup to a pyproject.toml one.