Add 529 plan contribution deductions/credits for OK, OR, PA, UT, VA, VT, WI (fix VA cap)

[MaxGhenis]

Summary

Implements 529 plan tax benefits for 7 states (SC and WV already implemented). This batch adds contribution deductions and/or credits for OK, OR, PA, UT, VA, VT, and WI, with special handling for state-specific rules and contribution caps.

Implementation details

State	Type	Cap
OK	Deduction	$10K single / $20K joint
OR	Refundable credit	$180 single / $360 joint
PA	Deduction	$19K per beneficiary
UT	Credit (4.55%)	Per beneficiary
VA	Deduction	$4K per account (capped)
VT	Credit (10%)	First $2,500/$5,000
WI	Deduction	$5,130 per beneficiary ($2,560 MFS)

Special cases

• OR: Tax credit instead of deduction ($180/$360 in 2025)
• UT: Non-refundable credit at 4.55% of contributions with per-beneficiary cap
• VT: Non-refundable credit at 10% of first $2,500/$5,000 contributed
• VA: Had existing implementation but was uncapped; now fixed with $4,000 per beneficiary cap

Closes

Closes #7554 (OK), #7557 (OR), #7559 (PA), #7563 (UT), #7566 (VA), #7568 (VT), #7572 (WI)

Test plan

• Verify contribution amounts within caps generate expected deductions/credits
• Verify excess contributions are not deducted/credited
• Verify state-specific rate calculations (OR at $180/$360, UT at 4.55%, VT at 10%)
• Verify VA cap correctly limits previously uncapped deductions
• Verify joint/single/MFS filer variations where applicable
• Run full test suite to ensure no regressions

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (55a0045) to head (9544667).
⚠️ Report is 37 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #7672      +/-   ##
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+ Coverage   97.82%   100.00%   +2.17%     
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  Files           3         9       +6     
  Lines          92       128      +36     
  Branches        2         0       -2     
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+ Hits           90       128      +38     
+ Misses          1         0       -1     
+ Partials        1         0       -1     

Flag	Coverage Δ
unittests	100.00% <100.00%> (+2.17%)	⬆️

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