Adding a non-metadata installer-only `dev-dependencies` table to pyproject.toml

[sinoroc]

@JacobCoffee, there is a very advanced proposal being worked on right now:

PEP 735: Dependency Groups in pyproject.toml

Hi all! This is my attempt to follow up on Projects that aren't meant to generate a wheel and `pyproject.toml` . Some notes and questions to seed discussion: I have mostly stayed close to @brettcannon’s proposed simplified solution from that thread, but have made a couple of changes. That’s part of why I listed him as sponsor, rather than co-author. It may be that his original, slightly simpler, proposal is preferable, but I think the draft PEP strikes the right balance between simplicit…

Or did I get things mixed up?