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 74.16%. Comparing base (3ddb69c) to head (a595c88).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7147       +/-   ##
===========================================
- Coverage   97.00%   74.16%   -22.84%     
===========================================
  Files           7     3663     +3656     
  Lines         100    52719    +52619     
  Branches        1      263      +262     
===========================================
+ Hits           97    39099    +39002     
- Misses          2    13584    +13582     
- Partials        1       36       +35     

Flag	Coverage Δ
unittests	74.16% <ø> (-22.84%)	⬇️

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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.