Exclude minor child earnings from NJ CCAP countable income (Closes #8074)

[MaxGhenis]

Summary

• Closes Followups: VA CCSP FDH rate age dimension; VA/NJ/CT CCAP countable-income child exclusions #8074 (Cluster B, NJ; last remaining fix in the issue).
• N.J.A.C. 10:15 does not enumerate an explicit statutory exclusion for minor children's earnings the way VA (8VAC20-790-40(H)) and CT (RCSA 17b-749-05(b)(2)(E)) do. However, the NJ CCAP application form CC-1 (03/24) Section D "Income" collects wage and self-employment income only from the applicant and co-applicant; there is no field for minor children's earnings. This operationalizes the exclusion in the CCR&R eligibility workflow even without an explicit regulation.

Changes

• Split countable_income.sources into:
  • earned_sources: employment_income, self_employment_income — summed only for tax-unit heads and spouses (the applicant/co-applicant on the CC-1).
  • unearned_sources: all other previously listed sources — summed across all members, since the CC-1 reports these at the family-unit level under "Other income or benefits to family unit".
• Replace nj_ccap_countable_income's declarative adds= with a formula that applies the head/spouse filter to earned income.
• Add 3 YAML regression tests: working teen's wages excluded, minor child entrepreneur's self-employment excluded, minor child's social_security_survivors (unearned) still counted.

Statutory / operational reference

• CCDF State Plan for NJ FFY 2025-2027, §2.2.4c (income definition): https://www.childcarenj.gov/ChildCareNJ/media/media_library/CCDF_State_Plan_for_New_Jersey_FFY25-27.pdf#page=25
• NJ CCAP Application CC-1 (03/24), Section D "Income" (per-applicant/co-applicant fields only): https://chsofnj.org/wp-content/uploads/2024/04/New-Jersey-Cares-for-Kids-Application-1.pdf#page=3

Note: If a future N.J.A.C. 10:15 update adds an explicit minor-earnings rule, update earned_sources.yaml with the precise cutoff.

Test plan

• policyengine-core test policyengine_us/tests/policy/baseline/gov/states/nj/njdhs/ccap/ -c policyengine_us — 134 passed (all CCAP tests green, including 3 new child-earnings cases).
• CI green.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (05d5d97) to head (de2afc3).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%            
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  Files           18         1    -17     
  Lines          353        17   -336     
  Branches         4         0     -4     
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- Hits           353        17   -336     

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

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[MaxGhenis]

Addressed reviewer feedback: switched the filter from is_tax_unit_head_or_spouse to age >= 18 (matching VA's 8VAC20-790-40(H)(10) exclusion rather than a narrower applicant-only rule). Added Case 9: an adult non-applicant relative's earnings still count (distinguishes the age rule from a narrower applicant/co-applicant-only rule). 9/9 tests pass locally.