Avoid state formula warning noise

[MaxGhenis]

Summary

• avoid divide-by-zero warnings in North Carolina TANF income eligibility
• replace the Pennsylvania TANF boolean inversion with a scalar-safe expression
• avoid invalid divide-by-zero arithmetic in Vermont military retirement phaseout without changing outputs
• add a North Carolina edge-case regression and changelog fragment

Validation

• PYTHONWARNINGS="error::RuntimeWarning,error::DeprecationWarning" UV_PYTHON=3.13 /opt/homebrew/bin/uv run python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/gov/states/nc/ncdhhs/tanf/nc_tanf_income_eligible.yaml policyengine_us/tests/policy/baseline/gov/states/pa/dhs/tanf/pa_tanf.yaml policyengine_us/tests/policy/baseline/gov/hhs/tanf/cash/tanf_negative_income_cap.yaml policyengine_us/tests/variables/gov/states/vt/tax/income/adjusted_gross_income/subtractions/retirement_income_exemption/vt_military_retirement_income_based_exemption.yaml -c policyengine_us
• /opt/homebrew/bin/ruff check policyengine_us/variables/gov/states/nc/ncdhhs/tanf/nc_tanf_income_eligible.py policyengine_us/variables/gov/states/pa/dhs/tanf/pa_tanf.py policyengine_us/variables/gov/states/vt/tax/income/adjusted_gross_income/subtractions/retirement_income_exemption/vt_military_retirement_income_based_exemption.py
• python3 -m py_compile policyengine_us/variables/gov/states/nc/ncdhhs/tanf/nc_tanf_income_eligible.py policyengine_us/variables/gov/states/pa/dhs/tanf/pa_tanf.py policyengine_us/variables/gov/states/vt/tax/income/adjusted_gross_income/subtractions/retirement_income_exemption/vt_military_retirement_income_based_exemption.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (fd8a1f8) to head (e026f32).
⚠️ Report is 38 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##              main     #7924    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           12         3     -9     
  Lines          174        61   -113     
==========================================
- Hits           174        61   -113     

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

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