Add aggregate_orders() function

- the function queries the database and aggregates the ad-hoc orders
  by pixel and time steps into a demand time series
- implement "heavy" integration tests for `aggregate_orders()`
- make `pandas` a package dependency
- streamline the `Config`

setup.cfg

@@ -138,6 +138,12 @@ per-file-ignores =
     src/urban_meal_delivery/db/utils/__init__.py:
         # Top-level of a sub-packages is intended to import a lot.
         F401,
+    src/urban_meal_delivery/forecasts/__init__.py:
+        # Top-level of a sub-packages is intended to import a lot.
+        F401,
+    src/urban_meal_delivery/forecasts/timify.py:
+        # No SQL injection as the inputs come from a safe source.
+        S608,
     tests/*.py:
         # Type annotations are not strictly enforced.
         ANN0, ANN2,
@@ -245,6 +251,8 @@ cache_dir = .cache/mypy
 ignore_missing_imports = true
 [mypy-packaging]
 ignore_missing_imports = true
+[mypy-pandas]
+ignore_missing_imports = true
 [mypy-pytest]
 ignore_missing_imports = true
 [mypy-sqlalchemy.*]