Fixes#369
Per the OCI Image Spec, manifest descriptor annotations are optional.
Previously, archives without annotations would fail to import with
"Failed to import image".
**Changes:**
- Modified `getImageReferencefromDescriptor` to return digest-based
references (`untagged@sha256:...`) when annotations are missing
- Removed guard that skipped manifests without annotations
- Added test case with `scratch_no_annotations.tar`
**Testing:**
All 167 tests pass, including new test for images without annotations.
RahulThennarasu
4d47c58a3d