Add `uv sync --dev-only` or equivalent

[charliermarsh]

This was a feature request, it seems reasonable to me.

[zanieb]

Including the root project, I presume? --only-dev for consistency with --with and --no-install?

[charliermarsh]

Yeah I prefer --only-dev. I was thinking exclusive of the root project but... I'm not sure?

[uptickmetachu]

We also need the ability to uv pip install pyproject.toml --dev (including dev requirements).

Necessary to install dev requirements into a docker containers --system.

[charliermarsh]

I wonder if this should instead be --prod and --no-prod, like --dev and --no-dev.

[zanieb]

I feel like --prod might imply something more, like ignoring "sources"?