Allow API partners to override SSI income for IL AABD calculation

[hua7450]

Summary

Fixes #7154

Adds a flag il_aabd_use_reported_ssi that allows API partners to override SSI income used in IL AABD calculations. This enables showing both federal SSI entitlement and IL AABD eligibility in a single API response.

Background

Illinois AABD (Aid to the Aged, Blind, and Disabled) counts federal SSI as unearned income. Since federal SSI typically exceeds IL AABD's need standard (~$822/month vs ~$943/month SSI), most SSI-eligible individuals are financially ineligible for AABD.

However, API partners want to show users:

1. How much they could receive from federal SSI (calculated ssi)
2. How much they could receive from IL AABD (if not receiving SSI)

Changes

New Variables

• il_aabd_use_reported_ssi - Boolean flag (default: False)
• il_aabd_ssi_income - Intermediate variable that selects between calculated ssi and ssi_reported

Modified Files

• gov/states/il/dhs/aabd/income/sources/unearned.yaml - Changed ssi → il_aabd_ssi_income

Usage

Default behavior (unchanged):

{
  "employment_income": 9600,
  "state_code": "IL"
}
// Output: ssi = $7,314, il_aabd = $0 (SSI makes person ineligible)

API partner override:

{
  "employment_income": 9600,
  "state_code": "IL",
  "ssi_reported": 0,
  "il_aabd_use_reported_ssi": true
}
// Output: ssi = $7,314 (entitlement), il_aabd = $6,264 (if not receiving SSI)

Test Coverage

• Unit tests for il_aabd_ssi_income (4 tests)
• Integration tests for API partner use cases (4 new tests):
  • Single person with ssi_reported: 0
  • Single person with partial ssi_reported
  • Parent with child
  • Couple (two eligible adults)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (1ceb893) to head (d1dec6c).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##              main     #7155     +/-   ##
===========================================
  Coverage   100.00%   100.00%             
===========================================
  Files            1         2      +1     
  Lines         3175        22   -3153     
===========================================
- Hits          3175        22   -3153     

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

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