feat: add durable store record serialization

src/user_engine/testing/store_conformance.py

@@ -89,6 +89,11 @@ def assert_user_engine_store_conformance(
     _assert_diagnostics_contract(testcase, store_factory)
 
 
+def reference_store_records(store: UserEngineStore) -> dict[str, Any]:
+    """Write and return a representative record for every store record type."""
+    return _write_reference_records(store)
+
+
 def _assert_readiness_contract(testcase: TestCase, store_factory: StoreFactory) -> None:
     store = store_factory()
     if store.schema_version is None: