Draft: API: remove UniqueResult, lower-case at, size for ResultSet

Summary

• Remove UniqueResult
• At and Size are lower-case now (ResultSet, MultiResultSet)

src/caosdb/entity.cpp

@@ -57,6 +57,10 @@ auto Parent::SetId(const std::string &id) -> void { this->wrapped->set_id(id); }
   return this->wrapped->name();
 }
 
+[[nodiscard]] auto Parent::GetDescription() const -> const std::string & {
+  return this->wrapped->description();
+}
+
 auto Parents::Append(const Parent &parent) -> void {
   auto *destination = this->wrapped->Add();
   destination->Swap(parent.wrapped);