Add unit tests workflow, including matrix of Python versions

[prjemian]

I'm not happy adding pins that do something already accomplished by package management software. We must not start that. Clearly conda can resolve the package requirements and it is not necessary to pin to a fixed version.

State your technical reasons.

Pinning makes sure that when the package is deployed, it is done so with the exact set of dependencies the team tested with. Bugs will still happen, but it’s much more reliable and consistent than using loose versioning, where the dependencies can vary and cause unexpected issues. As was shown above in Pyarrow not being able to be resolved.

Originally posted by @MDecarabas in #5 (comment)

[prjemian]

Widened the test matrix to all supported versions of Python that are also known to be supported by bluesky packages. (BS is not ready for Py3.13 yet.)

[prjemian]

Not testing yet with the queueserver. That can be an upgrade feature.