Define extra per `--package` with `uv sync`

[tlippold-meta]

Summary

When using uv sync --package=A --package=B and you want to install an extra of only one package, it is not possible AFAIK.

uv sync --package=A --package=B --extra=E installs the extra E of both packages.

uv sync --package=A[E] --package=B is not accepted by the parser:

invalid value 'A[E]' for '--package ': Not a valid package or extra name: "A[E]". Names must start and end with a letter or digit and may only contain -, _, ., and alphanumeric characters.

I would suggest accepting uv sync --package=A[E] --package=B if that is possible.

Example

uv sync --package=A[E] --package=B to install the extra E only of package A

[zanieb]

I don't think we want --package to accept extras but we could consider having --extra accept package[key, ...] 🤔

[tlippold-meta]

That would also be nice!