Add OrderHistory.time_step property

src/urban_meal_delivery/forecasts/timify.py

@@ -39,6 +39,11 @@ class OrderHistory:
         # The `_data` are populated by `.aggregate_orders()`.
         self._data = None
 
+    @property
+    def time_step(self) -> int:
+        """The length of one time step."""
+        return self._time_step
+
     @property
     def totals(self) -> pd.DataFrame:
         """The order totals by `Pixel` and `.time_step`.