- Add tests/crawler_core/test_boss_sign.py: 13 tests for BossSign, _compute_checksum, _generate_uuid
- Add tests/crawler_core/test_qcwy_sign.py: 10 tests for Job51Sign and SIGN_KEY
- Add tests/crawler_core/test_zhilian_sign.py: 13 tests for ZhilianSign
- Add conftest.py at project root to add project root to sys.path
- Update pyproject.toml with [tool.pytest.ini_options] pythonpath config
- Fix crawler_core/__init__.py: wrap heavy-dep imports in try/except so sign subpackages are importable in lightweight envs without requests_go installed
- Remove tests/crawler_core/__init__.py to prevent namespace shadowing of crawler_core package
