oci-image 0.3.0

OCI container images on disk: image references, sha256 digests, one-pass layer unpack (whiteouts and opaque directories), gzip (all cores via lgz one-pass streaming decode; small layers on one core) and zstd layers, a content-addressed store of blobs and per-layer directories in overlayfs format (each layer unpacked once, shared between images, refcounted, collected), and overlay snapshot prep.