Add healthcare state target diagnostics

[daphnehanse11]

Summary

• Add healthcare state target diagnostics to the US source coverage artifact.
• Report state coverage by role for ACA enrollment, ACA PTC recipients, ACA bronze/APTC plan choice, Medicaid enrollment, and Medicaid+CHIP enrollment.
• Add focused tests for state coverage counts and missing-state reporting.

Tests

• uv run pytest packages/populace-build/tests/test_us_fiscal_refresh_builder.py -q