feat: conditional swap using merkle proof

src/constants/BitMask.sol

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+uint256 constant MASK_1_BIT = 0x1;
+uint256 constant MASK_8_BITS = 0xff;
+uint256 constant MASK_24_BITS = 0xffffff;
+uint256 constant MASK_127_BITS = 0x7fffffffffffffffffffffffffffffff;
+uint256 constant MASK_128_BITS = 0xffffffffffffffffffffffffffffffff;
+uint160 constant MASK_160_BITS = 0x00ffffffffffffffffffffffffffffffffffffffff;
+
+uint256 constant MASK_BYTES_4 = 0xffffffff00000000000000000000000000000000000000000000000000000000;