Enable extracting individual dependencies

[paduszyk]

Issue Kind

Brand new capability

Description

I have recently come up with the idea that a useful feature would be to have the possibility of "extracting" individual dependencies with the versions read from either pyproject.toml or package.lock.

poetry install --extract PACKAGE

Impact

Sometimes, one needs to install a single package, preferably with the version consistent with Poetry's files.

For example, one may need ruff to lint and format their codebase in CI. ruff does not need anything except the codebase and itself.

If you put it to dev dependencies:

[tool.poetry.group.dev.dependencies]
# ...
ruff = "^0.6.7"
# ...

then you can install it by:

poetry install --only dev

but this will unnecessarily install other dev dependencies if any.

Workarounds

A workaround here is to define a separate group for a single dependency one would to "extract":

[tool.poetry.group.ruff.dependencies]
# ...
ruff = "^0.6.7"
# ...

Then:

poetry install --only ruff

handles the issue.

[finswimmer]

Duplicate of #3033