Slim source distributions via SwiftPM registries: a use case for exact version matching

This is a motivating use case and a request for feedback, not an Evolution proposal for a new registry protocol, version ordering rule, or dependency override API. Motivation Swift packages sometimes contain substantial development-only content, such as test fixtures, golden images, benchmarks, or unrelated projects in a monorepo. These files are useful to package maintainers but may be unnecessary for applications consuming the package. Downloading a source archive instead of cloning Git hist...