Add Marketplace premiums to SPM MOOP

[daphnehanse11]

Summary

• Adds marketplace_net_premium to spm_unit_medical_out_of_pocket_expenses.
• Updates the SPM MOOP documentation to list Marketplace, Medicaid, CHIP, and Medicare Part B computed premium components.
• Adds a selected-plan-ratio SPM MOOP test showing Marketplace net premium flows through after PTC.

Addresses #8095 and part of #8168.

Notes

This should be reviewed alongside the us-data residualization path in PolicyEngine/policyengine-us-data#844 so baseline imputed MOOP does not double-count computed Marketplace premiums.

Tests

• uv run python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/household/income/spm_unit/spm_unit_medical_out_of_pocket_expenses.yaml policyengine_us/tests/policy/baseline/household/income/spm_unit/spm_unit_medical_out_of_pocket_expenses_medicare_part_b.yaml policyengine_us/tests/policy/baseline/gov/aca/ptc/marketplace_net_premium.yaml -c policyengine_us
• uv run --extra dev ruff format policyengine_us/variables/household/income/spm_unit/spm_unit_medical_out_of_pocket_expenses.py
• uv run --extra dev ruff check policyengine_us/variables/household/income/spm_unit/spm_unit_medical_out_of_pocket_expenses.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (20705b0) to head (2fefbee).
⚠️ Report is 38 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##             main     #8178       +/-   ##
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+ Coverage   85.36%   100.00%   +14.63%     
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  Files           3         1        -2     
  Lines          41        16       -25     
  Branches        2         0        -2     
============================================
- Hits           35        16       -19     
+ Misses          6         0        -6     

Flag	Coverage Δ
unittests	100.00% <100.00%> (+14.63%)	⬆️

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[daphnehanse11]

Read-only review pass before patching:

The failing Full Suite - Baseline (irs-household) check is caused by the new marketplace_net_premium term flowing through spm_unit_medical_out_of_pocket_expenses into pre-existing household/SPM expense fixtures that were not setting ACA Marketplace inputs explicitly. The log shows:

• policyengine_us/tests/policy/baseline/household/cliff_gap.yaml: the two TX spm_unit_net_income@2021 expectations are now lower by 6675.7188, consistent with an added Marketplace net premium expense.
• policyengine_us/tests/policy/baseline/household/income/spm_unit/spm_unit_spm_expenses_chip_premium.yaml: spm_unit_spm_expenses@2024 now includes about 6294.821 of Marketplace net premium on top of the intended CHIP premium assertion.

I did not see a hardcoded-value, parameter metadata, or period-handling issue in the small formula diff itself. The focused fix is to isolate those existing non-Marketplace tests by explicitly setting Marketplace net premium/take-up to zero where the fixture is testing CHIP/cliff behavior, while leaving the new Marketplace SPM MOOP coverage intact.

Patching this now in a fresh detached worktree under /tmp.

[MaxGhenis]

This doublecounts marketplace premiums in MOOP and doesn't connect it to other MOOP use cases like SNAP and IMD. Fixing