[sethvargo]

Closes #308.

#286 moved helm_import_repository to repository_ctx.repo_metadata, but the toolchain repos still returned a bare dict. Bazel never put them in the repo contents cache, so every new output base downloaded and extracted helm again.

This change makes three rules return repo_metadata:

Rule	Returns
helm_toolchain_repository	reproducible = True when integrity is set, which the extension always does. Without it, the resolved integrity goes in attrs_for_reproducibility, the same as before.
helm_plugin_repository	reproducible = True when integrity is set. The attribute is mandatory.
helm_toolchain_repository_hub	reproducible = True. It only writes files from its attributes.

helm_host_alias_repository stays as it is because it reads repository_ctx.os. All three use the same hasattr guard as import.bzl, so Bazel 7 still gets the old return values.

Testing

On Bazel 9.3.1, I fetched the toolchain, with_cm_push, and plugin repos for darwin_arm64 into two fresh output bases that shared one --repository_cache. In both output bases, each repo was a symlink to the same repo contents cache entry. Before this change, the toolchain and plugin repos were real directories in every output base. buildifier -mode=check -lint=warn passes.

[abrisco]

Thank you!

[sethvargo]

@abrisco it looks like CI is failing, but I'm not entirely sure why?