Add CPS current health coverage anchors

[daphnehanse11]

Closes #629

Summary

• import current CPS NOW_* health coverage flags as reported at-interview coverage variables, including derived insured, uninsured, private/public, and multiple-coverage summaries
• keep compatibility aliases for existing marketplace and ESI inputs while expanding ACA and Medicaid coverage detail
• use reported marketplace and means-tested coverage as SSI/SNAP-style anchors for ACA and Medicaid take-up assignment in CPS, local-area publishing, and unified calibration rerandomization
• add tests for the new CPS coverage mappings and reported-anchor take-up behavior

Testing

• uv run pytest policyengine_us_data/tests/test_stochastic_variables.py policyengine_us_data/tests/test_calibration/test_unified_calibration.py policyengine_us_data/tests/test_datasets/test_cps.py -q