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

Makefile.am

@@ -97,6 +97,8 @@ unittest_sources = \
 	src/omemo/crypto.h \
 	src/omemo/store.h \
 	src/xmpp/vcard.h src/xmpp/vcard_funcs.h \
+	src/database_flatfile.h \
+	src/database_flatfile_parser.c \
 	src/command/cmd_defs.h src/command/cmd_defs.c \
 	src/command/cmd_funcs.h src/command/cmd_funcs.c \
 	src/command/cmd_ac.h src/command/cmd_ac.c \
@@ -172,6 +174,7 @@ unittest_sources = \
 	tests/unittests/test_callbacks.c tests/unittests/test_callbacks.h \
 	tests/unittests/test_plugins_disco.c tests/unittests/test_plugins_disco.h \
 	tests/unittests/test_forced_encryption.c tests/unittests/test_forced_encryption.h \
+	tests/unittests/test_database_export.c tests/unittests/test_database_export.h \
 	tests/unittests/unittests.c
 
 functionaltest_sources = \
@@ -191,6 +194,7 @@ functionaltest_sources = \
 	tests/functionaltests/test_disconnect.c tests/functionaltests/test_disconnect.h \
 	tests/functionaltests/test_history.c tests/functionaltests/test_history.h \
 	tests/functionaltests/test_lastactivity.c tests/functionaltests/test_lastactivity.h \
+	tests/functionaltests/test_export_import.c tests/functionaltests/test_export_import.h \
 	tests/functionaltests/functionaltests.c
 
 main_source = src/main.c