burrow owns the kernel catalog (KERNELS / Entry / resolve) and download
cache for the pichi-vm test suites. Consumers must use this catalog and must not
fork the table.
fetch(url) downloads a URL once into a cache directory under the cargo
target/ tree and returns the local path; later calls reuse it.
Keyed by URL, not content — a cache, not a verifier;
callers that need integrity pin the URL to an immutable artifact. Concurrent
callers are serialized per URL with an advisory file lock.
Intended as a dev-dependency for test suites that need real, cached fixtures (e.g. kernel images) without re-downloading on every run.
Apache-2.0 — see LICENSE.