Run black on all the notebooks

- we use black's default settings
- some cells are NOT kept in black's format to:
  - increase readability
  - or show Python's flexibility with regard to style

01_scientific_stack/03_exercises_simple_queries.ipynb

@@ -56,7 +56,7 @@
     "    \"orders.csv\",\n",
     "    index_col=\"order_id\",\n",
     "    dtype={\"cancelled\": bool},\n",
-    "    parse_dates=[\"placed_at\", \"pickup_at\", \"delivery_at\"]\n",
+    "    parse_dates=[\"placed_at\", \"pickup_at\", \"delivery_at\"],\n",
     ")"
    ]
   },