Sped up artist enrichment at least somewhat

tests/integration.rs

@@ -113,7 +113,24 @@ impl MetadataProvider for MockProvider {
         &self,
         _artist_mbid: &str,
     ) -> DataResult<Vec<shanty_tag::provider::ReleaseGroupEntry>> {
-        Ok(vec![])
+        Ok(vec![ReleaseGroupEntry {
+            mbid: "rg-123".into(),
+            title: "Test Album".into(),
+            primary_type: Some("Album".into()),
+            secondary_types: vec![],
+            first_release_date: Some("2024".into()),
+            first_release_mbid: Some("release-123".into()),
+        }])
+    }
+
+    async fn resolve_release_from_group(&self, release_group_mbid: &str) -> DataResult<String> {
+        if release_group_mbid == "rg-123" {
+            Ok("release-123".into())
+        } else {
+            Err(shanty_data::DataError::Other(format!(
+                "no releases for release-group {release_group_mbid}"
+            )))
+        }
     }
 }