CI workflows updated with setup-node v6

The CI infrastructure is receiving a version update. GitHub's setup-node action is being bumped from v4 to v6 across all three workflow files that handle continuous integration, publishing, and releases. This major version jump brings automatic package manager caching improvements and updates to internal dependencies. Workflows continue to use Node 22 with yarn caching enabled, so existing behavior is preserved while the underlying action gains the latest improvements and security patches accumulated since v4.