In-memory test registry doesn't support listing tags

In-memory test registry doesn't support listing tags: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). I'm using pkg/registry to spin up a local fake registry in my integration tests (via registry.New() ), which is great for exercising push/pull flows without a real…