Make RLP libraries unchecked regions consistent

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

@@ -592,8 +592,11 @@ library Lib_RLPReader {
         }
 
         // Pick out the remaining bytes.
+        uint256 mask;
         unchecked {
-            uint256 mask = 256 ** (32 - (_length % 32)) - 1;
+            mask = 256 ** (32 - (_length % 32)) - 1;
+        }
+
         assembly {
             mstore(
                 dest,
@@ -603,10 +606,8 @@ library Lib_RLPReader {
                 )
             )
         }
-
         return out;
     }
-    }
 
     /**
      * Copies an RLP item into bytes.

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

@@ -227,15 +227,16 @@ library Lib_RLPWriter {
             src += 32;
         }
 
+        uint256 mask;
         unchecked {
-            uint256 mask = 256 ** (32 - len) - 1;
+            mask = 256 ** (32 - len) - 1;
+        }
         assembly {
             let srcpart := and(mload(src), not(mask))
             let destpart := and(mload(dest), mask)
             mstore(dest, or(destpart, srcpart))
         }
     }
-    }
 
     /**
      * Flattens a list of byte strings into one byte string.