Update Medicaid work requirement implementation

[daphnehanse11]

Summary:

• Scope Medicaid work requirement gating to the ACA adult Medicaid category instead of all Medicaid categories.
• Add currently modelable CMS/law exclusions and safe harbors: earned-income threshold, half-time student status, pregnant/postpartum medical assistance, former foster care under 26, Medicare eligibility, and incarceration.
• Refresh parameter citations/descriptions and add targeted eligibility tests.

Audit notes:

• H.R. 1 became Public Law 119-21 on July 4, 2025.
• CMS published the Dec. 8, 2025 CMCS Informational Bulletin on Medicaid community engagement requirements.
• I did not find a published Medicaid community engagement interim final rule as of May 11, 2026.

Tests:

• uv run python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/hhs/medicaid/eligibility --batches 1
• uv run python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/hhs/medicaid --batches 1
• git diff --check -- touched Medicaid work requirement files

[daphnehanse11]

Superseded by the upstream PolicyEngine PR: PolicyEngine#8257