Update Missouri 2025 Individual Income Tax Model

[DTrim99]

Closes #7146

Summary

Updates Missouri income tax model for tax year 2025:

• Add 2025 references to all tax parameters
• Update mo_max_social_security_benefit with 2025 value
• Add 2025 test cases

Changes

• Tax rates and brackets - add 2025 references
• Deductions - add 2025 references
• Credits - add 2025 references
• Property tax credit - add 2025 references
• Tests for 2025

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.97%. Comparing base (66ccff2) to head (4c08559).
⚠️ Report is 510 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7147      +/-   ##
==========================================
+ Coverage   72.72%   73.97%   +1.25%     
==========================================
  Files        3757     3757              
  Lines       54115    54115              
  Branches      267      267              
==========================================
+ Hits        39353    40033     +680     
+ Misses      14742    14046     -696     
- Partials       20       36      +16     

Flag	Coverage Δ
unittests	73.97% <ø> (+1.25%)	⬆️

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[hua7450]

Just a note: there are changes for 2026 property tax, might need to update parameter files for it. https://revisor.mo.gov/main/OneSection.aspx?section=135.030&bid=57542

[DTrim99]

Fixes Applied

🟡 Reviewer Feedback Addressed

• ✅ 2026 Property Tax Credit Parameters: Added all 2026 values per @hua7450's review comment referencing MO Rev Stat § 135.030

Changes Made

Modified Files:

• property_tax_limit.yaml: Added 2026-01-01 value of $1,550 (up from $1,100)
• rent_property_tax_limit.yaml: Added 2026-01-01 value of $1,055 (up from $750)

New Parameters Created:

• credit_calculation_base.yaml: Base amount for credit calculation ($1,055 for 2026)
• upper_income_limit/single.yaml: $38,200
• upper_income_limit/single_homestead.yaml: $42,200
• upper_income_limit/married.yaml: $41,000
• upper_income_limit/married_homestead.yaml: $48,000

Verification

• ✅ All 15 MO property tax credit tests pass
• ✅ Code formatted with make format

Note: The new upper income limit parameters are created but not yet integrated into the variable formulas. The 2026 formula changes may require updates to mo_property_tax_credit.py to use these filing-status-specific limits instead of the current phaseout logic. This can be addressed in a follow-up PR when the 2026 forms are released.

[PavelMakarchuk]

General comment: I think we added new parameter files which are not used in any formula, please check

[DTrim99]

Fixes Applied

🔴 Review Feedback Addressed

Pavel's Comment: "I think we added new parameter files which are not used in any formula, please check"

• ✅ Removed unused 2026 property tax credit parameters

  The following parameter files were added for 2026 law changes but were not yet integrated into any formula:

  • credit_calculation_base.yaml
  • upper_income_limit/single.yaml
  • upper_income_limit/single_homestead.yaml
  • upper_income_limit/married.yaml
  • upper_income_limit/married_homestead.yaml

  These have been removed. They can be re-added in a follow-up PR when the mo_property_tax_credit.py formula is updated to use the new filing-status-specific income limits required for 2026.

Verification

• ✅ Code formatted with make format
• ✅ Changes pushed to branch

Ready for re-review.