Enforce partnership S-corp leaf exports

[MaxGhenis]

Closes #35.

Summary

• declare PUF tax-detail outputs as the partnership_income and s_corp_income leaves plus partnership_self_employment_net_earnings instead of the partnership_s_corp_income aggregate
• make the PolicyEngine-US adapter exclude partnership_s_corp_income from accepted input variables and reject it on export, even while the current PE-US wheel still reports it as an input
• update engine-backed round-trip tests to prove the leaves persist and the aggregate is absent/blocked

Validation

• env -u UV_FROZEN uv run --python 3.13 ruff format --check .
• env -u UV_FROZEN uv run --python 3.13 ruff check .
• git diff --check
• env -u UV_FROZEN uv run --python 3.13 --all-packages --all-groups --all-extras python -m pytest packages/populace-frame/tests/test_policyengine_us_adapter.py packages/populace-build/tests/test_us_plan.py -q
• env -u UV_FROZEN uv run --python 3.13 --all-packages --all-groups --all-extras python -m pytest packages/populace-frame/tests packages/populace-build/tests -q

Review

• /cycle subagent review found no actionable findings; added the suggested explicit assertion that the reloaded H5 does not contain partnership_s_corp_income.