message: perf: skip tree operations when no tree output is requested
diff: @@ -836,8 +836,8 @@ void run(
  *outputJsonStream << serializeResults(results);
  }
  - const auto &tree = nextclade.finalize(results);
  if (outputTreeStream) {
  + const auto &tree = nextclade.finalize(results);
  (*outputTreeStream) << tree.serialize();
  }
  }
  