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/caosdb_test_utility.h

@@ -33,16 +33,16 @@
  */
 #define EXPECT_THROW_MESSAGE(statement, exeption_type, message)                \
   EXPECT_THROW(                                                                \
-      try { statement; } catch (const exeption_type &e) {                      \
-        EXPECT_EQ(std::string(e.what()), message);                             \
-        throw;                                                                 \
-      },                                                                       \
-      exeption_type)
+    try { statement; } catch (const exeption_type &e) {                        \
+      EXPECT_EQ(std::string(e.what()), message);                               \
+      throw;                                                                   \
+    },                                                                         \
+    exeption_type)
 #define ASSERT_THROW_MESSAGE(statement, exeption_type, message)                \
   ASSERT_THROW(                                                                \
-      try { statement; } catch (const exeption_type &e) {                      \
-        ASSERT_EQ(std::string(e.what()), message);                             \
-        throw;                                                                 \
-      },                                                                       \
-      exeption_type)
+    try { statement; } catch (const exeption_type &e) {                        \
+      ASSERT_EQ(std::string(e.what()), message);                               \
+      throw;                                                                   \
+    },                                                                         \
+    exeption_type)
 #endif