PEP 723: use a new `[run]` table instead of `[project]`?

Pants has the notion of applying an interpreter constraint to every python file. I could see us scraping this new field to populate that metadata on behalf of the user.

That being said, my vote is still that this is given piecemeal. First we decide on a format (because we haven’t done that yet) in a way that most people are ok with (Ofek wants toml, Paul’s OK with it but not pyproject.toml, Brett’s working on user surveys, and then everyones comments on the 3 threads). Then we can decide what goes in. It seems this discussion is starting to mirror, somewhat, Projects that aren't meant to generate a wheel and `pyproject.toml` so perhaps that’s not a coincidence?

I think for this to be the smoothest sailing, we might want to try and tackle each sub problem, or else we’re stuck discussing how to format things, or decide on multiple fields on PEPs dedicated to getting single-file scripts runnable.