Proto generation plugins are scoped to avoid breaking Swift-less CI

The SwiftPM-based protoc plugins used to generate Tuist’s vendored proto code are no longer declared as global mise tools. They are resolved on demand only inside the proto-generation tasks, so a plain mise install on a Swift-less Linux runner no longer tries to build them. This restores CLI Canary Release and other Linux workflows that were failing because they auto-install the full toolchain but never need the Swift plugins.