refactor(tvix/castore): switch to ingest_entries for tarball ingestion

With `ingest_entries` being more generalized, we can now use it for
ingesting the directory entries generated from tarballs.

Change-Id: Ie1f7a915c456045762e05fcc9af45771f121eb43
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11489
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

tvix/castore/src/import/mod.rs

@@ -199,6 +199,7 @@ where
     Ok(digest)
 }
 
+#[derive(Debug, Clone, Eq, PartialEq)]
 pub enum IngestionEntry {
     Regular {
         path: PathBuf,
@@ -228,4 +229,8 @@ impl IngestionEntry {
             IngestionEntry::Unknown { path, .. } => path,
         }
     }
+
+    fn is_dir(&self) -> bool {
+        matches!(self, IngestionEntry::Dir { .. })
+    }
 }