Residualize modeled health premiums

[daphnehanse11]

Summary

• Adds a CPS data-generation step that residualizes imputed health premium inputs by subtracting baseline computed premiums when the installed policyengine-us exposes them.
• Allocates tax-unit-level computed premiums, such as CHIP, Marketplace, and Medicaid premiums, to the first person in each tax unit before subtracting from person-level imputed premiums.
• Adds unit tests for residual math and tax-unit-to-person allocation.

Addresses PolicyEngine/policyengine-us#8089.

Notes

The residualization step is version-gated so current builds remain safe when a computed premium variable is not present in the locked policyengine-us version. This creates the us-data path needed for computed premium reforms to replace, rather than double-count with, baseline imputed MOOP components.

Tests

• uv run pytest tests/unit/datasets/test_health_premium_residualization.py tests/unit/datasets/test_marketplace_plan_benchmark_ratio.py tests/unit/test_medicare_part_b_inputs.py
• uv run ruff format .
• uv run ruff format --check .
• uv lock --locked
• uv run ruff check policyengine_us_data/datasets/cps/cps.py tests/unit/datasets/test_health_premium_residualization.py

Full uv run ruff check . was also run; it fails on existing unrelated lint issues across notebooks, Modal scripts, long-term projection scripts, and tests.