feat: add balancer v2 executor

foundry/lib/balancer-labs/v2-interfaces/contracts/standalone-utils/IstETH.sol

@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+pragma solidity >=0.7.0 <0.9.0;
+
+import "../solidity-utils/openzeppelin/IERC20.sol";
+
+// solhint-disable-next-line max-line-length
+// Based on https://github.com/lidofinance/lido-dao/blob/816bf1d0995ba5cfdfc264de4acda34a7fe93eba/contracts/0.4.24/Lido.sol
+
+interface IstETH is IERC20 {
+    function submit(address referral) external payable returns (uint256);
+}