Use github actions for creating binaries and adding signatures

The new "github actions" might provide a way to automatically create and sign binaries.
Automating this could speed up publishing binaries after tagging a release, and we'd have an additional set of signatures.

The issue names no files, workflows, tests, or entry points. Review the repository's current reproducible build, binary publishing, and signing process, then assess how GitHub Actions could automate it after a release tag. Done means the approach is implemented, produces binaries, and adds verifiable signatures.

Written by the indexing model from the issue text.