fix: optimize LightAccountFactory's _getCombinedSalt

Author: jaypaik

src/LightAccountFactory.sol

@@ -45,7 +45,11 @@ contract LightAccountFactory {
         );
     }
 
-    function _getCombinedSalt(address owner, uint256 salt) internal pure returns (bytes32) {
-        return keccak256(abi.encode(owner, salt));
+    function _getCombinedSalt(address owner, uint256 salt) internal pure returns (bytes32 combinedSalt) {
+        assembly ("memory-safe") {
+            mstore(0x00, owner)
+            mstore(0x20, salt)
+            combinedSalt := keccak256(0x00, 0x40)
+        }
     }
 }

test/LightAccount.t.sol

@@ -288,7 +288,7 @@ contract LightAccountTest is Test {
                     bytes32(uint256(uint160(0x0000000071727De22E5E9d8BAf0edAc6f37da032)))
                 )
             ),
-            0x61ded19e9e86ff20a3a8822529fb98ef584c1e9f6e1457dcfdcd1f5e146d7d97
+            0xa677af8a16ab66d988856a88ea647c45da368a588b036126ce3e21645f7891ca
         );
     }