[INFRA] Test import as part of ci

[lmeyerov]

Is your feature request related to a problem? Please describe.

Every month or two we get a failed release b/c unit tests pass, but something wrong with the exports means post-install import actually fails. E.g., #550 .

Describe the solution you'd like

As part of ci + publish, we should test a flow of pip install ... => import graphistry; print(graphistry.__version__)

• ci: we can likely do a pip install -i http://... using the git checkout hash => github url
• publish: after the test.pypi.org publish, we can do a pip install -i http://test.pypi.org/... of the specific version