Hi,
I recently made an observation that ScalarType::parseValue() is called twice for custom scalars.
This is due to webonyx/graphql already resolving ScalarType and EnumType by itself while GraphQLite is trying to resolve it again. Obviously this observation already has been made for Enums but not for Scalars:
GraphQL\Utils\Value

TheCodingMachine\GraphQLite\Types\ArgumentResolver

I guess the second resolve call can be omitted then if we have a ScalarType :)