feat: Implement release manifests

[davidkern]

This PR enables the nix repo to be integrated with the Upwind Sensor automated release workflow.

• Adds a release/ directory containing json manifest files for each released version. New manifests will be checked-in to this directory as part of automation;
• Adds a release.nix module to read from the proper manifests and construct attributes that are passed to the package downloader;
• Provides a generate-manifest.sh script to create manifest files;
• Introduces unit tests for the new release module, using runTests;
• Adds some check, lint, and test recipes to a Justfile, and adds a Github workflow to run these on PRs.