docs: add natspec for helpers

solidity/test/utils/Helpers.sol

@@ -61,11 +61,22 @@ contract Helpers is DSTestPlus {
     _id = keccak256(abi.encode(_dispute));
   }
 
+  /**
+   * @notice Creates a mock contract, labels it and erases the bytecode
+   *
+   * @param _label The label to use for the mock contract
+   * @return _contract The address of the mock contract
+   */
   function _mockContract(string memory _label) internal returns (address _contract) {
     _contract = makeAddr(_label);
     vm.etch(_contract, hex'69');
   }
 
+  /**
+   * @notice Sets an expectation for an event to be emitted
+   *
+   * @param _contract The contract to expect the event on
+   */
   function _expectEmit(address _contract) internal {
     vm.expectEmit(true, true, true, true, _contract);
   }