Propagate partnership/S-corp income split (policyengine-us#8614) into the US build

[MaxGhenis]

Background

policyengine-us#8614 split partnership/S-corp income and reshaped the SE variable:

• partnership_s_corp_income is now a formula-owned aggregate (adds = [partnership_income, s_corp_income]).
• New input leaves: partnership_income, s_corp_income.
• partnership_se_income was renamed to partnership_self_employment_net_earnings.

Populace exports model input variables and imputes them from the PUF/source pipeline, so it must produce the leaves rather than the engine-computed aggregate.

Work needed

1. Export contract: do not export partnership_s_corp_income as an input. The formula-owned export checks merged in Fix Populace release and export gates #37 cover this class.
2. Values: impute/populate partnership_income and s_corp_income, and rename the SE column to partnership_self_employment_net_earnings in the current Populace build/profile surface.
3. Verification: run the current export/source/gate suite with the leaves populated and the aggregate omitted.

Acceptance criteria

• partnership_income and s_corp_income are populated from the source pipeline.
• partnership_self_employment_net_earnings replaces the old SE column name where applicable.
• partnership_s_corp_income is not persisted as a final input.
• Tests cover the leaf variables and formula-owned aggregate rejection.