This commit improves the performance and consistency of the salary tools:
- Redundant query normalization and word extraction are eliminated in salary_lookup.py by pre-calculating representations once before the search loop.
- A match_score_optimized helper is introduced to perform the comparison using the pre-calculated query data, preserving full backward compatibility for match_score.
- Normalization in tools/convert_salary_excel.py is unified: paired column headers now consistently substitute spaces and dashes with underscores (e.g. 'software_engineering') to match the single-column formatting.
- Unit test coverage is significantly expanded in tests/test_salary_lookup.py and tests/test_convert_salary_excel.py to cover normalization, anglicization, search filtering, and matching behaviors.
