Add WIC calibration targets

[MaxGhenis]

Summary

• Add FY 2024 national WIC total-cost and participation calibration targets from USDA FNS WIC Program Data.
• Include the national WIC dollar target and person_count for wic > 0 in the training target config.
• Cover WIC target loading and target-config inclusion in unit tests.

Source

USDA FNS exact workbook: WIC Program Participation and Costs, National Level Annual Summary, sheet Annual Participation and costs, FY 2024 row. The workbook is linked from the FNS WIC Data Tables page under National Level Annual Summary and has data as of April 10, 2026.

FY 2024 values used:

• Total participation: 6.704 million average monthly participants
• Total costs: $7.3322B

Also shown in the same row but not used as the dollar target:

• Food costs: $4.9115B

Validation

• uv run ruff format --check policyengine_us_data/db/etl_national_targets.py tests/unit/test_etl_national_targets.py tests/unit/calibration/test_target_config.py
• uv run ruff check policyengine_us_data/db/etl_national_targets.py tests/unit/test_etl_national_targets.py tests/unit/calibration/test_target_config.py
• uv run pytest tests/unit/test_etl_national_targets.py tests/unit/calibration/test_target_config.py
• uv run python - <<'PY' ... extract_national_targets(year=2024) ... PY