feat: update _handleCallback, add verifyCallback with docs

foundry/interfaces/ICallback.sol

@@ -2,7 +2,24 @@
 pragma solidity ^0.8.26;
 
 interface ICallback {
+    /**
+     * @notice Handles callback data from a protocol or contract interaction.
+     * @dev This method processes callback data and returns a result. Implementations
+     * should handle the specific callback logic required by the protocol.
+     *
+     * @param data The encoded callback data to be processed.
+     * @return result The encoded result of the callback processing.
+     */
     function handleCallback(
         bytes calldata data
     ) external returns (bytes memory result);
+
+    /**
+     * @notice Verifies the validity of callback data.
+     * @dev This view function checks if the provided callback data is valid according
+     * to the protocol's requirements. It should revert if the data is invalid.
+     *
+     * @param data The encoded callback data to verify.
+     */
+    function verifyCallback(bytes calldata data) external view;
 }