pub async fn fetch_formula(formula: &str) -> Result<Formula>Expand description
Fetch and parse a formula through the package index.
Resolves against packages.zlayer.dev (or ZLAYER_PACKAGE_INDEX_URL) with a
formulae.brew.sh fallback. The version is not hardcoded — a formula bump
is picked up automatically — and the resolved formula now carries
urls.stable.checksum (the source-tarball sha256).
§Errors
Returns crate::error::ToolchainError::RegistryError if the formula cannot
be fetched or parsed from either the index or the upstream.