Upload release assets with the GitHub CLI (#46)

Release assets are now attached by gh release upload in the build job,
replacing the third-party action that ran in the publish job. They are
attached before publishing to PyPI, so a failure there still leaves a
complete release, and --clobber makes the step safe to re-run.

Merge pull request #5 from harp-tech/refactor-unified-api

Refactor package for unified data and device API