Surround operation with unchecked to use wrapping arithmetic

https://docs.soliditylang.org/en/v0.8.0/control-structures.html#checked-or-unchecked-arithmetic

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

@@ -592,6 +592,7 @@ library Lib_RLPReader {
         }
 
         // Pick out the remaining bytes.
+        unchecked {
             uint256 mask = 256 ** (32 - (_length % 32)) - 1;
             assembly {
                 mstore(
@@ -605,6 +606,7 @@ library Lib_RLPReader {
 
             return out;
         }
+    }
 
     /**
      * Copies an RLP item into bytes.

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

@@ -228,6 +228,7 @@ library Lib_RLPWriter {
             src += 32;
         }
 
+        unchecked {
             uint256 mask = 256 ** (32 - len) - 1;
             assembly {
                 let srcpart := and(mload(src), not(mask))
@@ -235,6 +236,7 @@ library Lib_RLPWriter {
                 mstore(dest, or(destpart, srcpart))
             }
         }
+    }
 
     /**
      * Flattens a list of byte strings into one byte string.