Make never_eligible_for_social_security_benefits an input

[MaxGhenis]

Fixes #7799

Related: PolicyEngine/policyengine-taxsim#765

Summary

• remove the heuristic that inferred permanent Social Security ineligibility from age and missing SS income
• make never_eligible_for_social_security_benefits an explicit boolean input with a default of False
• add a New Jersey regression covering the TAXSIM discrepancy

Testing

• uv run python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/gov/ssa/ss/never_eligible_for_social_security_benefits.yaml policyengine_us/tests/policy/baseline/gov/states/nj/tax/income/exclusions/nj_other_retirement_special_exclusion.yaml policyengine_us/tests/policy/baseline/gov/states/nj/tax/income/integration.yaml -c policyengine_us

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (6e5759e) to head (646c308).
⚠️ Report is 2989 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##             main     #7833       +/-   ##
============================================
+ Coverage   73.43%   100.00%   +26.56%     
============================================
  Files        3943         1     -3942     
  Lines       56969         7    -56962     
  Branches      277         0      -277     
============================================
- Hits        41836         7    -41829     
+ Misses      15101         0    -15101     
+ Partials       32         0       -32     

Flag	Coverage Δ
unittests	100.00% <100.00%> (+26.56%)	⬆️

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