Function extract_diff_ids 

pub fn extract_diff_ids(
    media_type: &MediaType,
    config_reader: impl Read,
    manifest_layers: &[Descriptor],
) -> Result<Vec<OciDigest>>

Extract ordered diff_ids from a config descriptor.

For standard container images (ImageConfig media type), parses the config JSON and returns rootfs.diff_ids. For artifacts with non-standard config types, falls back to using manifest layer digests as identifiers. Note: oci-spec models diff_ids as Vec<String> but they are actually OCI content digests. We parse them here so the rest of the codebase can work with the strongly-typed Digest.