Fix Georgia retirement exclusion capital loss handling

[PavelMakarchuk]

Summary

Fixes #7951.

Georgia's retirement income exclusion was using raw person-level capital_gains, which let unlimited capital losses wipe out the exclusion. It also summed earned income and other retirement income in one bucket, even though Schedule 1 Page 2 floors those amounts separately before applying the age-based cap.

Changes

• add ga_retirement_exclusion_countable_capital_gains, backed by federal loss-limited person capital gains
• update retirement exclusion sources to use the loss-limited capital gains input instead of raw capital_gains
• refactor ga_retirement_income_exclusion_retirement_income to match the worksheet:
  • floor countable earned income at zero
  • floor lines 6-13 income at zero
  • add the two floored amounts together
• floor the final person exclusion at zero in ga_retirement_exclusion_person
• add regressions for:
  • the policyengine-taxsim Add parameter indicating status of program implementation #757 large-capital-loss case
  • a simpler case where earned income should still qualify even when capital losses drive other retirement income negative

Why this structure

The durable fix is broader than swapping one source variable. Georgia Schedule 1 Page 2 treats earned income and the remaining retirement income sources as separate worksheet sections, each with its own zero floor, before combining them. Matching that structure prevents capital losses from incorrectly offsetting countable earned income.

Verification

• python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/ga/tax/income/subtractions/retirement/ga_retirement_income_exclusion_retirement_income.yaml --batches 1
• python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/ga/tax/income/integration.yaml --batches 1
• python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/ga/tax/income/subtractions/retirement --batches 1
• python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/ga/tax/income --batches 1

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (e8a542a) to head (dee4c7a).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #7955   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         3    +2     
  Lines           17        41   +24     
=========================================
+ Hits            17        41   +24     

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

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[DTrim99]

Reviewed the Georgia retirement exclusion capital-loss fix. I did not find any actionable issues.

I checked the refactored retirement-income aggregate, the updated source list, the new loss-limited capital-gains wrapper, the per-person exclusion clamp, and the new regression coverage against the 2024 IT-511 Schedule 1 worksheet structure. The separation between line 5 earned income and line 14 non-earned retirement income matches the form.