Support lock dependencies with lowest solvable versions

• I have searched the issues of this repo and believe that this is not a duplicate.
• I have searched the documentation and believe that my question is not covered.

Feature Request

Context

When I am implementing a library, it would be super useful to run my tests with all the supported dependencies defined with the constrains in pyproject.toml. This will prevent errors in production when, for example, I use some new features of a dependency and forget to update the dependencies constrains (this is hard to identify when you are coding).

Because running the tests with all the possible combinations of all your supported libraries is virtually impossible, maybe running them with the lowest versions solvable solution and also the highest (I think this is the default behavior)

Proposal

• add the flag --use-lowest-versions to the cli entrypoints (install, sync, lock, shell, and run)
• these commands will create and/or use a different lock file poetry.lowest.lock
• a different venv will be created by just adding lowest after the project name like this: {project_name}-lowest-{id}-{python-version}

Main simple use case

In ci do the following steps

• Install environments

>>> poetry install 
>>> poetry install --use-lowest-versions

• run tests for highest versions

poetry run pytest  --junit-xml pytest.xml

• run tests for lowest versions

poetry run --use-lowest-versions pytest  --junit-xml pytest.xml

Note: I would appreciate if anyone has a better name for the flag (naming is the hardest part :P)

Also, I looked a the code and I think I know where add this logic, I can create a PR if you like the idea

Start by reviewing the CLI entrypoints named in the proposal—install, sync, lock, shell, and run—alongside the existing lock-file and virtual-environment behavior. Done means supporting a lowest-solvable dependency mode with a separate lock file and environment, plus the documented CI commands working for both highest and lowest versions.