feat: oci compliance work (#85)

* chore: rework oci crate to be more composable

* feat: image pull is now internally explicit

* feat: utilize vfs for assembling oci images

* feat: rework oci to preserve permissions via a vfs

crates/oci/src/packer/mod.rs

@@ -0,0 +1,58 @@
+use std::path::PathBuf;
+
+use self::backend::OciPackerBackendType;
+use oci_spec::image::{ImageConfiguration, ImageManifest};
+
+pub mod backend;
+pub mod cache;
+pub mod service;
+
+#[derive(Debug, Default, Clone, Copy)]
+pub enum OciPackedFormat {
+    #[default]
+    Squashfs,
+    Erofs,
+}
+
+impl OciPackedFormat {
+    pub fn extension(&self) -> &str {
+        match self {
+            OciPackedFormat::Squashfs => "squashfs",
+            OciPackedFormat::Erofs => "erofs",
+        }
+    }
+
+    pub fn backend(&self) -> OciPackerBackendType {
+        match self {
+            OciPackedFormat::Squashfs => OciPackerBackendType::MkSquashfs,
+            OciPackedFormat::Erofs => OciPackerBackendType::MkfsErofs,
+        }
+    }
+}
+
+#[derive(Clone)]
+pub struct OciImagePacked {
+    pub digest: String,
+    pub path: PathBuf,
+    pub format: OciPackedFormat,
+    pub config: ImageConfiguration,
+    pub manifest: ImageManifest,
+}
+
+impl OciImagePacked {
+    pub fn new(
+        digest: String,
+        path: PathBuf,
+        format: OciPackedFormat,
+        config: ImageConfiguration,
+        manifest: ImageManifest,
+    ) -> OciImagePacked {
+        OciImagePacked {
+            digest,
+            path,
+            format,
+            config,
+            manifest,
+        }
+    }
+}