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.
We were doing intermediate step copies to Data objects both for push and
pull. We only need the data for the lifetime of the singular writes to
update the state of the checksums and to write to disk somewhere, so we
can use a view into the buffer from the http client to satisfy this.
Resolves the warning
```
LocalOCILayoutClient.swift:87:37: warning: capture of non-sendable type 'T.AsyncIterator.Type' in an isolated closure
87 | for try await buffer in input {
| `- warning: capture of non-sendable type 'T.AsyncIterator.Type' in an isolated closure
88 | wrote += buffer.readableBytes
89 | try buffer.withUnsafeReadableBytes { pointer in
```
Signed-off-by: Aditya Ramani <a_ramani@apple.com>
Dmitry Kovba