/// Integration tests for relationship persistence, loading, and raw DB-layer edge operations.
///
/// - `persistence_tests` — dirty tracking and commit behaviour for both relationship
/// backends (`bevy_many_relationships` and Bevy-native), side by side.
/// - `loading_tests` — loading persisted relationships back into ECS; covers
/// `bevy_many_relationships` (hydrator, `PersistentQuery`, `schedule_load`) and
/// Bevy-native (`with_relationship_depth` + registered loader) in two `#[cfg]` modules.
/// - `db_tests` — raw database-layer edge CRUD and query operations,
/// independent of Bevy ECS and the persistence plugin.