feat: add V1 custody accounting

test/mocks/FeeOnTransferToken.sol

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.35;
+
+import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
+
+contract FeeOnTransferToken is ERC20 {
+    constructor() ERC20("Fee-on-Transfer Token", "FOT") {}
+
+    function decimals() public pure override returns (uint8) {
+        return 6;
+    }
+
+    function mint(address to, uint256 amount) external {
+        _mint(to, amount);
+    }
+
+    function transferFrom(address from, address to, uint256 amount) public override returns (bool) {
+        address spender = _msgSender();
+        _spendAllowance(from, spender, amount);
+
+        uint256 received = amount * 99 / 100;
+        _transfer(from, to, received);
+        _burn(from, amount - received);
+        return true;
+    }
+}