Fix DC CDCC rate to 24.25% for TY2026+ (currently 32%)

[MaxGhenis]

Summary

Fixes #7677.

DC Code § 47-1806.04(c)(1)(B), as amended by the Fiscal Year 2025 Budget Support Act of 2024 (D.C. Act 25-506, sec. 7032, signed July 15, 2024), requires the DC CDCC match rate to drop from 32% to 24.25% for tax years beginning after December 31, 2025.

The statute states:

"(B) For each full calendar or fiscal year beginning after December 31, 2025, there is allowed a credit against the tax imposed by § 47-1806.03 in an amount equal to 24.25% of the amount of the credit to which the resident may be entitled under section 21 of the Internal Revenue Code of 1986"

Changes

• Added 2026-01-01: 0.2425 entry to match.yaml
• Added statute reference to the parameter metadata
• Added two new test cases: TY2025 (still 32%) and TY2026 (24.25%)

Test plan

• Existing TY2021 and TY2022 tests continue to pass at 32%
• New TY2025 test confirms 32% rate still applies
• New TY2026 test confirms 24.25% rate applies

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.45%. Comparing base (55a0045) to head (7754ac9).
⚠️ Report is 37 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7683       +/-   ##
===========================================
- Coverage   97.82%   73.45%   -24.37%     
===========================================
  Files           3     3904     +3901     
  Lines          92    56341    +56249     
  Branches        2      271      +269     
===========================================
+ Hits           90    41387    +41297     
- Misses          1    14932    +14931     
- Partials        1       22       +21     

Flag	Coverage Δ
unittests	73.45% <ø> (-24.37%)	⬇️

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