Revert #8911: restore OK retirement subtraction for IRC 401 pensions pre-2022 (#9009)

[PavelMakarchuk]

Fixes #9009. Reverts #8911 (which addressed #8830).

Problem

#8911 excluded private (IRC §401) employer pensions from ok_pension_subtraction before 2022, on the premise that the 2021 Schedule 511-A line 6 instructions did not list §401 plans. That premise is false. The 2021 Form 511 Packet, page 17 — the same document cited by private_pension_qualifies.yaml — lists as the first qualifying source "An employee pension benefit plan under IRC Section 401". The 2022 packet's line-6 text is word-for-word identical; §401 was not added in 2022.

Effect on the originating taxsim record (2021 MFJ, pensions $38,458): PolicyEngine returned ok_pension_subtraction = $0 (should be 2 × $10,000 = $20,000) and overstated ok_income_tax by a flat $1,000 (5% × $20,000) for any pre-2022 MFJ record with ≥$10k/person private pension.

Fix

Reverts #8911: drops the private_pension_qualifies gate and restores min_(p.pension_limit, pensions) per person.

Tests

• Unit: added a 2021 case confirming a private (IRC §401) pension qualifies for the $10,000 exclusion. Removed the incorrect 2021 "private → $0" case introduced by Exclude private (IRC 401) employer pensions from OK retirement subtraction before 2022 #8911.
• Integration: added the taxsim New York #1083 case → ok_pension_subtraction $20,000, ok_agi $61,891, ok_income_tax $2,005 (matches TaxAct and TAXSIM-35 to the dollar).

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (ff39625) to head (82133f8).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #9016   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            1         1           
  Lines           18        14    -4     
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- Hits            18        14    -4     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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