Update PolicyEngine US to 1.691.12

[policyengine]

Summary

Update PolicyEngine US from 1.691.3 to 1.691.12.

What changed (1.691.3 -> 1.691.12)

Changed

• Apply Arkansas HB1001 (2026 1st Extraordinary Session) individual income tax rate cuts effective tax year 2026.

Fixed

• Extend the CRFB non-refundable Social Security credit reform so it continues feeding into non-refundable credits after 2035.
• Subtract Form 4952 investment-income elections from net capital gain for the federal capital-gains tax.
• Update the 2026 Social Security payroll cap to the official SSA contribution and benefit base.
• Fix asset stock variables being divided across months in SNAP categorical eligibility calculations.
• Fixed the Nebraska refundable Child Tax Credit child-care eligibility proxy to read tax_unit_childcare_expenses (populated by typical tax filers) instead of pre_subsidy_childcare_expenses (only populated by benefits-program calculations).
• Fixed the AMT capital-gains calculation to read the regular-tax ordinary-income portion (Schedule D Tax Worksheet line 14 / line 21) for Form 6251 Part III line 27, so that filers whose AMTI minus exemption is below the 20% LTCG bracket threshold no longer overflow gains into the 20% bracket.
• Set explicit 2025 Maine property tax fairness credit benefit-base values to match the published Schedule PTFC/STFC line 8 table ($2,550 single / $3,300 HoH-one-child or joint-no-child / $4,050 joint or HoH-multi / $4,100 senior). IRS uprating with downwards $50 rounding produced values $50 short.
• Applied the 2025 federal-AGI-based phaseout to the Maine non-military pension income deduction.
• Adjust the Kentucky family size tax credit rate brackets at the 1.27 and 1.33 boundaries to account for KY's 0.5-cent rounding-up convention in the Schedule ITC table.
• Fix tax_unit_itemizes tied-federal-tax fallback to compare federal standard against federal itemized deductions, restoring TaxAct/TAXSIM behavior and resolving downstream CO/VT/LA state-tax discrepancies.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.01%. Comparing base (661538d) to head (e66d6fc).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3580   +/-   ##
=======================================
  Coverage   78.01%   78.01%           
=======================================
  Files          67       67           
  Lines        4071     4071           
  Branches      759      759           
=======================================
  Hits         3176     3176           
  Misses        700      700           
  Partials      195      195           

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