fix(client): Update type hints in Microgrid class for better clarity

- Changed type hints for `delivery_area` and `location` attributes in the `Microgrid` class to support `DeliveryArea | None` and `Location | None`.
- This modification enhances type safety and improves code readability.

Signed-off-by: eduardiazf <[email protected]>

Author: eduardiazf

src/frequenz/client/assets/types.py

@@ -119,11 +119,11 @@ def from_protobuf(pb: PBMicrogrid) -> "Microgrid":
         Returns:
             A new Microgrid instance populated with data from the protobuf message.
         """
-        delivery_area: DeliveryArea = None
+        delivery_area: DeliveryArea | None = None
         if pb.HasField("delivery_area"):
             delivery_area = DeliveryArea.from_protobuf(pb.delivery_area)
 
-        location: Location = None
+        location: Location | None = None
         if pb.HasField("location"):
             location = Location.from_protobuf(pb.location)