chore: mypy for strong_typing

Mostly just ignores because of the dynamic nature of the codebase. One
prominent change is expanding the allowed types for attributes tracking
property types to allow strings (which are valid and common typing hints
in python).

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>

llama_stack/strong_typing/serializer.py

@@ -134,7 +134,10 @@ class IPv6Serializer(Serializer[ipaddress.IPv6Address]):
 
 class EnumSerializer(Serializer[enum.Enum]):
     def generate(self, obj: enum.Enum) -> Union[int, str]:
-        return obj.value
+        value = obj.value
+        if isinstance(value, int):
+            return value
+        return str(value)
 
 
 class UntypedListSerializer(Serializer[list]):