In the ZapRouterBase.sol, the _transferStEthToCaller function uses two different methods for transferring stETH depending on whether its wrapped or not:
While this implementation isnt necessarily incorrect, it doesnt consistently use the share-based transfer method for stETH, which could potentially lead to slight discrepancies if a rebasing event occurs between the calculation of _stEthVal and the actual transfer.
To ensure consistent and rebasing-resistant behavior, modify the _transferStEthToCaller function to use transferShares for unwrapped stETH transfers.
