Switch from flit to PDM

[astrojuanlu]

I've been using PDM lately for some new projects and I really like it.

Like flit, it has a pdm init command with a nice CLI wizard, it's standards-compliant, and largely transparent.

Unlike flit, it's extensible through plugins, has the ability of extracting the version from git, and does not rely on the __version__ attribute, which I like (pretty much like the Pallets projects, I am migrating away from it getsentry/sentry-python#2316)

Why not Pipenv? Because it's a 1st-generation workflow tool and we have collectively learned a lot from it. It tries to do too much, and badly. And unfortunately it has a cursed history IMHO (I prefer to stay away from certain maintainers).

Why not Poetry? Because, as a 2nd-generation tool that predates some packaging standards, it suffers from python-poetry/poetry#3332. And their npm-esque way of specifying upper version caps is causing so much grief in the ecosystem.

Why not Hatch? Even as a 3rd-generation tool (very much like PDM), I don't like pypa/hatch#507. I trust PDM much more.

Why not some 4th-generation tool, like rye or huak? Because they're still experimental.

[ofek]

For posterity, Hatch has supported building projects that use arbitrary backends since 1.8.0 https://hatch.pypa.io/latest/history/hatch/#hatch-v1.8.0