fix: ensure entity col name is passed to the valueframe in legacy spec

src/timeseriesflattener/feature_specs/from_legacy.py

@@ -95,7 +95,8 @@ def create_combinations(self) -> Sequence[v2_specs.PredictorSpec]:
                                     ): self.entity_id_col_name_out,
                                 },
                                 axis=1,
-                            )
+                            ),
+                            entity_id_col_name=self.entity_id_col_name_out,
                         ),
                         lookbehind_distances=lookbehind_days,
                         fallback=fallback,  # noqa: B023