At this stage Zig version updates introduce multiple breaking changes. So long as rules_zig supports only a single Zig version at a time, any Zig version update requires a big-bang migration of a whole project. Ideally, it would be possible to upgrade in smaller more incremental steps. Use an approach as demonstrated in https://github.com/aherrmann/2024-04-10-bazel-toolchain-version-constraint to support multiple Zig versions within a single build.

• register multiple Zig versions
• select Zig version via build setting
• support version transitions
• sort versions by semver ordering
• don't specify a version in the core module, but set a default if no module sets a version
• allow the root module to specify a default version
• simplify the Zig version integration test
• generate config settings for version ranges, e.g. 0.11 to capture 0.11.0, 0.11.1, etc.