Make RLP libraries unchecked regions consistent

packages/contracts/contracts/libraries/rlp/Lib_RLPReader.sol

@@ -592,20 +592,21 @@ library Lib_RLPReader {
         }
 
         // Pick out the remaining bytes.
+        uint256 mask;
         unchecked {
-            uint256 mask = 256 ** (32 - (_length % 32)) - 1;
-            assembly {
-                mstore(
-                    dest,
-                    or(
-                        and(mload(src), not(mask)),
-                        and(mload(dest), mask)
-                    )
-                )
-            }
+            mask = 256 ** (32 - (_length % 32)) - 1;
+        }
 
-            return out;
+        assembly {
+            mstore(
+                dest,
+                or(
+                    and(mload(src), not(mask)),
+                    and(mload(dest), mask)
+                )
+            )
         }
+        return out;
     }
 
     /**

packages/contracts/contracts/libraries/rlp/Lib_RLPWriter.sol

@@ -227,13 +227,14 @@ library Lib_RLPWriter {
             src += 32;
         }
 
+        uint256 mask;
         unchecked {
-            uint256 mask = 256 ** (32 - len) - 1;
-            assembly {
-                let srcpart := and(mload(src), not(mask))
-                let destpart := and(mload(dest), mask)
-                mstore(dest, or(destpart, srcpart))
-            }
+            mask = 256 ** (32 - len) - 1;
+        }
+        assembly {
+            let srcpart := and(mload(src), not(mask))
+            let destpart := and(mload(dest), mask)
+            mstore(dest, or(destpart, srcpart))
         }
     }