Add New Mexico SSI state supplement

[MaxGhenis]

Summary

Implements the New Mexico SSI State Supplement, a flat $100/month payment for SSI recipients living in licensed Adult Residential Shelter Care Homes (ARSCH). Replaces #7346 (rebased from upstream/main to resolve conflicts).

Closes #7345

Regulatory authority

• Statute: NMSA 1978, Section 27-2-9.1
• Regulations: 8.106.500.10 NMAC (effective March 1, 2025)
• Administering agency: New Mexico Health Care Authority (HCA), Income Support Division

Eligibility criteria (8.106.500.10 NMAC)

1. Must be receiving SSI under Title XVI
2. Must reside in a licensed ARSCH facility
3. Must be age 18 or older

Benefit calculation

If eligible: $100/month x 12 = $1,200/year
If not eligible: $0

Files added/modified

• 2 parameter files (amount, min_age)
• 3 variable files (eligibility, benefit, is_in_adult_residential_care input)
• 3 test files (18 test cases)
• Modified household_state_benefits.yaml

Test plan

• All YAML tests written with step-by-step comments
• make format passes
• CI passes on GitHub

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (2dd3b64) to head (5e906de).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #7456   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         3    +1     
  Lines           24        35   +11     
=========================================
+ Hits            24        35   +11     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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