Refactor test methods in test_format_sv.py

[coderabbitai]

As discussed in this comment, it's suggested to refactor long test methods into smaller, focused test cases in test/format_tests/test_format_sv.py.\n\nPR: https://github.com/OpenVoiceOS/ovos-date-parser/pull/51\nRequester: @JarbasAl