Data consumer callback

The callback for data consuming contract must have the following type signature (the method name can be arbitrary)

function processResponse(uint256 receivedRequestId, DataItem memory response, IdType idType) external;

Here receivedRequestId is either id of the previously created request (in case of on-chain initiation), or id of the data flow (in case of off-chain initiation). These two cases can be distinguished by looking at the idType. response contains the data from the oracle. As a data consumer, upon the data receiving, one must ensure that + The method was called by the Quex Core contract + idType has the expected value + receivedRequestId has the expected value

The optional checks include + Verify that error code in response is zero (depending on the particular oracle pool capabilities) + Verify that the timestamp in the response is within tolerance bound (depending on the oracle pool policies, data transfer mode, and business logic)