State supplements under SSI spousal deeming should compare individual and couple state computations (POMS SI 01320.430) #10149

Found during the independent review of #10141. This was already on main; #10141 doesn't change it.

Several federally administered state supplements reduce the supplement by the federal SSI shortfall, max(0, -uncapped_ssi):

• policyengine_us/variables/gov/states/de/dhss/ssp/de_ssp.py
• policyengine_us/variables/gov/states/dc/dhcf/ossp/dc_ossp.py
• policyengine_us/variables/gov/states/hi/dhs/oss/hi_oss.py
• policyengine_us/variables/gov/states/ma/dta/ssp/ma_state_supplement.py

POMS SI 01320.430 D.1–D.3 covers an eligible individual living with an ineligible spouse when deeming applies. It says the state supplement is computed separately on an individual basis and on a couple basis, and the state then applies its own lesser-of comparison. 20 CFR 416.1163(d)(2)(iii) points to 416.2025(b).

Reviewer's example for Delaware (2026), not yet re-run: the claimant has no income, and the ineligible spouse has a pension of $1,531 a month. Combined countable income is $1,511, which leaves a federal shortfall of $20. The model pays $120. The state comparison gives min(140, 448 − 20) = $140.

Tasks:

• Check the example against Delaware's parameters.
• Implement both bases and the comparison for each state.
• Add YAML cases with values hand-computed from POMS and each state's payment levels.