ytLending supports USDC as the base token

contracts/ytLending/Lending.sol

@@ -156,7 +156,7 @@ contract Lending is
     function supply(uint256 amount) external override nonReentrant whenNotPaused {
         accrueInterest();
         
-        IERC20(baseToken).safeTransferFrom(msg.sender, address(this), amount);
+        IERC20(baseToken).transferFrom(msg.sender, address(this), amount);
         
         // 获取用户当前本金
         UserBasic memory user = userBasic[msg.sender];
@@ -240,7 +240,7 @@ contract Lending is
         uint256 newTotal = userCollateral[msg.sender][asset] + amount;
         if (newTotal > config.supplyCap) revert SupplyCapExceeded();
         
-        IERC20(asset).safeTransferFrom(msg.sender, address(this), amount);
+        IERC20(asset).transferFrom(msg.sender, address(this), amount);
         
         userCollateral[msg.sender][asset] += amount;
         
@@ -440,7 +440,7 @@ contract Lending is
         if (collateralAmount > collateralReserves[asset]) revert InsufficientBalance();
         
         // 收取清算人支付的资金
-        IERC20(baseToken).safeTransferFrom(msg.sender, address(this), baseAmount);
+        IERC20(baseToken).transferFrom(msg.sender, address(this), baseAmount);
         
         // 抵押品出库
         collateralReserves[asset] -= collateralAmount;
@@ -673,5 +673,11 @@ contract Lending is
         
         emit WithdrawReserves(to, amount);
     }
+
+    /**
+     * @dev 预留存储空间，用于未来升级时添加新的状态变量
+     * 50个slot = 50 * 32 bytes = 1600 bytes
+     */
+    uint256[50] private __gap;
 }