Skip publishing when all package versions are published

[JoviDeCroock]

Summary

• add a reusable .github/scripts/has-unpublished-packages.mjs check for publishable package versions
• expose the check as a release job output
• skip the gated publish job when Changesets has no release PR to create and all current versions are already on npm

Testing

• GITHUB_OUTPUT=/tmp/publish-check-output node .github/scripts/has-unpublished-packages.mjs

[changeset-bot]

⚠️ No Changeset found

Latest commit: b200a36

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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