message: Add index_bvh[_inst|_ref]_t.num_indices()
diff: @@ -230,6 +230,7 @@ public:
  VSNRAY_FUNC size_t num_primitives() const { return primitives_last - primitives_first; }
  VSNRAY_FUNC size_t num_nodes() const { return nodes_last - nodes_first; }
  + VSNRAY_FUNC size_t num_indices() const { return indices_last - indices_first; }
  VSNRAY_FUNC P& primitive(size_t indirect_index) const
  {
  @@ -352,6 +353,11 @@ public:
  return ref_.num_nodes();
  }
  + VSNRAY_FUNC size_t num_indices() const
  + {
  + return ref_.num_indices();
  + }
  +
  VSNRAY_FUNC P& primitive(size_t indirect_index) const
  {
  return ref_.primitive(indirect_index);
  @@ -524,6 +530,7 @@ public:
  size_t num_primitives() const { return primitives_.size(); }
  size_t num_nodes() const { return nodes_.size(); }
  + size_t num_indices() const { return indices_.size(); }
  bvh_ref ref() const
  {
  