Ship Go binaries inside per-platform npm packages (@alibaba-group/ocr-{os}-{arch})
so npm install resolves the correct binary via optionalDependencies + os/cpu fields.
This removes the need for a postinstall download from GitHub Releases, which is
extremely slow for users behind restricted networks (e.g. China mainland).
The postinstall download is retained as a fallback for --no-optional installs.