Add CI workflow that tests using conda libsemigroups

[Joseph-Edwards]

This PR adds a workflow that tests libsemigroups_pybind11 against the conda version of libsemigroups. It also moves the linting into its own workflow.

Supersedes #240.

[Joseph-Edwards]

The Conda tests are failing because we haven't made a release of libsemigroups since adding the balance (and friends) functions. This is expected.

Arguably, it is too aggressive to run the tests for Conda and GitHub whenever we make a PR, since we might not mind if some of them fail. We could instead only check against GitHub libsemigroups for PRs into main, and against Conda libsemigroups for PRs into Stable branches.

On the other hand, it serves as a good reminder to make regular small releases, so I'm not sure what's best.

[james-d-mitchell]

I'm happy enough for us to include these tests, but maybe we can scale them back to only testing ubuntu/mac-latest, python 3.13, since what are we testing here exactly? That we haven't become incompatible with the release versions of libsemigroups (good to know), and that we work with condo install libsemigroups (also good to know), neither of these involve the version of python (as far as I can tell), so maybe there's no point in testing all of these versions.

[Joseph-Edwards]

The reason for testing all of the versions is for making sure the Python code we've written is compatible with all of the versions of Python. For example, when we started adding typing support, we needed to check it was valid for the older versions of Python.

That said, I agree that we don't need to cheek all of the versions twice.

I think it's probably best to check all of the versions against GitHub libsemigroups, and only the conda one once. What do you think @james-d-mitchell?