Question - Publishing OCI Artifacts - Should the layer be compressed?

I am currently building a new supporting tool and just wondering if this is correct.

```shell
$ oras pull ghcr.io/devcontainers/features/git:latest
Downloading ebd18821c6cc devcontainer-feature-git.tgz
Downloaded ebd18821c6cc devcontainer-feature-git.tgz
Pulled [registry] ghcr.io/devcontainers/features/git:latest
Digest: sha256:f839be8a0203abe12c917b262b1a1330b8286f9576ef21ea4a26ed60c5bc9947
$ file devcontainer-feature-git.tgz
devcontainer-feature-git.tgz: POSIX tar archive
```

Inspecting the layer manually reveals that the _media type_ is `application/vnd.devcontainers.layer.v1+tar`. However, the filename from the `org.opencontainers.image.title` annotation gives a ".tgz" extension. The actual file does not seem to be compressed.

I'm just wondering which is actually correct? A bare tar archive? Or a gzip'd compressed version?