message: fix: use `double` type explicitly in divergence calculations
  In order to avoid integer truncation
diff: @@ -165,17 +165,17 @@ namespace Nextclade {
  }
  - const auto baseDiv = node.divergence().value_or(0);
  + const double baseDiv = node.divergence().value_or(0.0);
  // HACK: Guess the unit of measurement of divergence.
  // Taken from: https://github.com/nextstrain/auspice/blob/6a2d0f276fccf05bfc7084608bb0010a79086c83/src/components/tree/phyloTree/renderers.js#L376
  // FIXME: Should be resolved upstream in augur/auspice.
  constexpr const auto HACK_MAX_DIVERGENCE_THRESHOLD = 5;
  - auto thisDiv = totalNucMutations;// unit: number of substitutions
  + double thisDiv = totalNucMutations;// unit: number of substitutions
  if (maxDivergence <= HACK_MAX_DIVERGENCE_THRESHOLD) {
  thisDiv /= rootSeq.size();// unit: number of substitutions per site
  }
  - const auto divergence = baseDiv + thisDiv;
  + const double divergence = baseDiv + thisDiv;
  nucMutations.shrink_to_fit();
  