Add functional and unit tests for DB export/import

- 2 functional tests: export_sqlite_to_flatfile, import_flatfile_to_sqlite
  with XEP-0203 delay timestamps for deterministic verification
- 27 unit tests for database_export covering edge cases
- Merge test/db-functional-tests: 12 DB persistence tests (test_history)
- Group 2 rebalanced: 25 tests (23 base + 2 SQLite-only export/import)
- #ifdef HAVE_SQLITE guards for export/import tests
- prof_stop() helper in proftest.c
- Makefile.am: source ordering cleanup, new test files added

tests/functionaltests/test_history.c

@@ -385,7 +385,6 @@ message_db_history_service_chars(void **state)
     assert_true(prof_output_exact("svc: a\\b c|d e%f {g} [h] i=j"));
 }
 
-#ifdef HAVE_HISTORY_VERIFY
 /*
  * Test: /history verify reports no issues after normal message writes.
  */
@@ -416,7 +415,6 @@ message_db_history_verify(void **state)
     prof_input("/history verify");
     assert_true(prof_output_exact("Verification complete: no issues found."));
 }
-#endif /* HAVE_HISTORY_VERIFY */
 
 /*
  * Test: LMC (Last Message Correction, XEP-0308) — incoming correction