make pricedb currency mandatory

now, if there is a price entry for an ingredient, it either has to have a currency specified or default_currency has to be set in settings.yaml

comfyrecipes/parsing.py

@@ -564,7 +564,7 @@ class PriceDB(Element):
         price: float,
         amount: float,
         unit: Unit,
-        currency: Optional[str],
+        currency: str,
     ) -> None:
         super().__init__(ctx)
         self.price = price
@@ -591,4 +591,6 @@ class PriceDB(Element):
         currency = ctx.settings.default_currency
         if "currency" in dct:
             currency = dct["currency"]
+        if currency is None:
+            raise RuntimeError("currency not specified and default_currency is also not set")
         return cls(ctx=ctx, price=price, amount=amount, unit=unit, currency=currency)