private static boolean isTimestampMember(Model model, Shape shape) {
        return shape.asMemberShape()
                .map(MemberShape::getTarget)
                .flatMap(model::getShape)
                .filter(Shape::isTimestampShape)
                .isPresent();
    }
Requires that the value provided for all timestamp shapes is a
unix timestamp.
smithy-model/src/main/java/software/amazon/smithy/model/validation/node/TimestampValidationStrategy.java