feat(Verifier): add contract for post-attack storage verification

Adds a minimal Verifier contract that checks if a target contract's
deepest storage slot was updated to the expected attack value. This
enables the test to verify attack success without expensive post-state
checks on all attacked contracts.

The verify() function calls getDeepest() on the target and compares
the returned value against the expected attack value.

Author: CPerezz

tests/benchmark/stateful/bloatnet/depth_benchmarks/Verifier.sol

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+/**
+ * @title Verifier
+ * @dev Minimal contract to verify that an attacked contract's deep storage slot was updated.
+ *      Called at the end of the attack execution to confirm the attack succeeded.
+ */
+contract Verifier {
+    /**
+     * @dev Verifies that the target contract's deepest storage slot contains the expected value.
+     * @param target The address of the attacked contract
+     * @param expectedValue The expected value in the deep storage slot
+     * @return success True if the value matches, false otherwise
+     */
+    function verify(address target, uint256 expectedValue) external view returns (bool success) {
+        // Call getDeepest() on target - selector is 0x77b5b7e6
+        // bytes4(keccak256("getDeepest()")) = 0x77b5b7e6
+        (bool callSuccess, bytes memory data) = target.staticcall(
+            abi.encodeWithSelector(0x77b5b7e6)
+        );
+
+        if (!callSuccess || data.length != 32) {
+            return false;
+        }
+
+        uint256 actualValue = abi.decode(data, (uint256));
+        return actualValue == expectedValue;
+    }
+}