feat: add storage-safe bank V2

src/BankV1.sol

@@ -30,7 +30,7 @@ contract BankV1 is Initializable, UUPSUpgradeable, OwnableUpgradeable, PausableU
         _disableInitializers();
     }
 
-    function initialize(address asset_, address initialOwner) external initializer {
+    function initialize(address asset_, address initialOwner) public initializer {
         if (asset_ == address(0)) {
             revert InvalidAsset(asset_);
         }

src/BankV2.sol

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.35;
+
+import {BankV1} from "./BankV1.sol";
+
+/// @custom:oz-upgrades-from src/BankV1.sol:BankV1
+contract BankV2 is BankV1 {
+    event BalanceTransferred(address indexed from, address indexed to, uint256 amount);
+
+    error InvalidRecipient(address recipient);
+    error SelfTransfer();
+
+    function transferBalance(address recipient, uint256 amount) external whenNotPaused {
+        if (amount == 0) revert ZeroAmount();
+        if (recipient == address(0)) revert InvalidRecipient(recipient);
+        if (recipient == msg.sender) revert SelfTransfer();
+        uint256 available = _balances[msg.sender];
+        if (amount > available) {
+            revert InsufficientBalance(msg.sender, available, amount);
+        }
+        _balances[msg.sender] = available - amount;
+        _balances[recipient] += amount;
+        emit BalanceTransferred(msg.sender, recipient, amount);
+    }
+
+    function contractVersion() public pure override returns (uint256) {
+        return 2;
+    }
+}