fix(spells): backfill casting times for all imported spells

data/spells/purify_food_and_drink.json

@@ -5,6 +5,7 @@
   "range": "close",
   "save": "will",
   "base_dc": 10,
+  "cast_time": "standard",
   "effects": [],
   "description": "A cantrip: cleanses 1 cu. ft./level of spoiled, rotten, diseased or poisoned food and water, making it pure and drinkable (no effect on creatures or magic potions). Will negates (object). Non-combat utility: the engine does not model objects, so the spell has no mechanical effects here."
 }