DataFetcher<Optional<Integer>> getProtocolVersionDataFetcher() {
    return dataFetchingEnvironment -> Optional.of(highestEthVersion);
  }
Returns a DataFetcher that fetches the highest Ethereum protocol version supported by the node.

<p>The DataFetcher is a functional interface. It has a single method that takes a
DataFetchingEnvironment object as input and returns the highest Ethereum protocol version as an
Optional<Integer>.

@return a DataFetcher that fetches the highest Ethereum protocol version
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/graphql/GraphQLDataFetchers.java