Medicaid CE: model state-optional hardship exceptions

Parent issue: #7751

The Medicaid community engagement rules include hardship or exception concepts that are better handled separately from permanent exclusions and direct compliance. This should be its own design and implementation thread because several pieces require external or state-specific data.

Scope:
- Identify which hardship exceptions are mandatory versus state-optional under CMS guidance.
- Add state parameters for optional hardship categories only where needed.
- Decide which inputs are explicit person-level booleans and which can be derived from data.
- Consider county unemployment and federal disaster data separately before adding derived variables.
- Add tests for each implemented hardship path and for states that do not elect an optional hardship.

Candidate hardship categories from #7751:
- Hospitalization or intensive services.
- County unemployment threshold.
- Federal disaster declaration.
- Long-distance medical travel.

Out of scope:
- Application or renewal review-period mechanics.
- Data pipeline work unless a specific derived hardship is selected.

Sources:
- https://www.congress.gov/bill/119th-congress/house-bill/1/text
- https://www.medicaid.gov/federal-policy-guidance/downloads/cib12082025.pdf