ENH: Test datatypes and values in Extern C interface

Integration tests for https://gitlab.indiscale.com/caosdb/customers/lfpb/management/-/issues/420 and caosdb-cpplib!13 (merged)

Almost solely whitespace changes that my clang-tidy performed, the only real changes concern the way strings are "returned" by the Extern C interface.

test/test_transaction.cpp

@@ -72,7 +72,7 @@ protected:
 
     // delete all entities
     const auto &connection =
-        caosdb::connection::ConnectionManager::GetDefaultConnection();
+      caosdb::connection::ConnectionManager::GetDefaultConnection();
     auto query_transaction(connection->CreateTransaction());
     query_transaction->Query("FIND ENTITY WITH id > 99");
     query_transaction->Execute();
@@ -94,7 +94,7 @@ protected:
  */
 TEST_F(test_transaction, retrieve_non_existing) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   auto transaction(connection->CreateTransaction());
 
@@ -124,7 +124,7 @@ TEST_F(test_transaction, retrieve_non_existing) {
  */
 TEST_F(test_transaction, insert_without_delete) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   auto insert_transaction(connection->CreateTransaction());
 
@@ -159,7 +159,7 @@ TEST_F(test_transaction, insert_delete) {
   // same as in insert_without_delete
   // until marked  END SAME
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   auto insert_transaction(connection->CreateTransaction());
 
@@ -204,7 +204,7 @@ TEST_F(test_transaction, insert_delete_with_parent) {
   // same as in insert_without_delete
   // until marked  END SAME
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   auto insert_transaction(connection->CreateTransaction());
 
@@ -299,7 +299,7 @@ TEST_F(test_transaction, insert_delete_with_parent) {
  */
 TEST_F(test_transaction, insert_delete_with_property) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   // Create and insert property
   Entity prop_ent;
@@ -435,7 +435,7 @@ TEST_F(test_transaction, insert_delete_with_property) {
  */
 TEST_F(test_transaction, test_multi_retrieve) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   auto transaction(connection->CreateTransaction());
 
@@ -469,7 +469,7 @@ TEST_F(test_transaction, test_multi_retrieve) {
  */
 TEST_F(test_transaction, insert_update_delete) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   // INSERT
   auto insert_transaction(connection->CreateTransaction());
@@ -537,7 +537,7 @@ TEST_F(test_transaction, insert_update_delete) {
  */
 TEST_F(test_transaction, test_query) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   auto insert_transaction(connection->CreateTransaction());
 
@@ -583,7 +583,7 @@ TEST_F(test_transaction, test_query) {
  */
 TEST_F(test_transaction, test_query_with_retrieve) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   // rt1
   Entity rt1;
@@ -698,7 +698,7 @@ TEST_F(test_transaction, test_query_with_retrieve) {
  */
 TEST_F(test_transaction, test_file_upload) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   Entity file;
   file.SetRole(Role::FILE);
@@ -735,7 +735,7 @@ TEST_F(test_transaction, test_file_upload) {
  */
 TEST_F(test_transaction, test_file_up_n_download) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   Entity file;
   file.SetRole(Role::FILE);
@@ -754,7 +754,7 @@ TEST_F(test_transaction, test_file_up_n_download) {
 
   auto download_transaction(connection->CreateTransaction());
   download_transaction->RetrieveAndDownloadFilesById(
-      inserted_file.GetId(), test_download_file_1.string());
+    inserted_file.GetId(), test_download_file_1.string());
   download_transaction->ExecuteAsynchronously();
   ASSERT_EQ(download_transaction->WaitForIt().GetCode(), StatusCode::SUCCESS);
 
@@ -781,7 +781,7 @@ TEST_F(test_transaction, test_file_up_n_download) {
  */
 TEST_F(test_transaction, test_full_workflow) {
   const auto &connection =
-      caosdb::connection::ConnectionManager::GetDefaultConnection();
+    caosdb::connection::ConnectionManager::GetDefaultConnection();
 
   // ######  Create Data Model  ######
   Entity dataRT;