add return value name in interface for estimateTCO2RedemptionAmount

Co-authored-by: Michalis Kargakis <kargakis@protonmail.com>

src/interfaces/IFeeCalculator.sol

@@ -44,5 +44,5 @@ interface IFeeCalculator {
     function estimateTCO2RedemptionAmount(address pool, address tco2, uint256 poolAmount)
         external
         view
-        returns (uint256);
+        returns (uint256 estimatedTCO2Amount);
 }