Implement recoverable exact result deletion

crates/remora-target/src/store.rs

@@ -413,6 +413,14 @@ impl TargetStore {
         self.multipart.abort(&session.identity).await
     }
 
+    pub async fn abort_multipart_exact(
+        &self,
+        identity: &MultipartIdentity,
+    ) -> Result<(), TargetError> {
+        self.ensure_multipart_identity(identity)?;
+        self.multipart.abort(identity).await
+    }
+
     pub async fn discover_staging_write(
         &self,
         key: &str,