message: rpc: Speedup getrawmempool when verbose=true
diff: @@ -474,7 +474,10 @@ UniValue MempoolToJSON(const CTxMemPool& pool, bool verbose)
  const uint256& hash = e.GetTx().GetHash();
  UniValue info(UniValue::VOBJ);
  entryToJSON(pool, info, e);
  - o.pushKV(hash.ToString(), info);
  + // Mempool has unique entries so there is no advantage in using
  + // UniValue::pushKV, which checks if the key already exists in O(N).
  + // UniValue::__pushKV is used instead which currently is O(1).
  + o.__pushKV(hash.ToString(), info);
  }
  return o;
  } else {
  