message: fix: avoid copying std::pair
diff: @@ -95,7 +95,7 @@ namespace Nextclade {
  mutatedPositions.insert(seqSub.pos);
  }
  - for (const auto [pos, refNuc] : nodeSubstitutions) {
  + for (const auto& [pos, refNuc] : nodeSubstitutions) {
  if (!has(mutatedPositions, pos) && isSequenced(pos, seq)) {
  const auto& queryNuc = rootSeq[pos];
  privateMutations.emplace_back(NucleotideSubstitution{
  