Prepare certified US state/year artifacts with temporary ACS WIC compatibility

[anth-volk]

Fixes #560

The separate removal draft is #563. It is blocked on the replacement dataset
tracked in PolicyEngine/microcosm#1154.

Changes

• Include the existing opt-in prototype commits for verified, lossless US source partitioning and shared state/year preparation. These are preparation artifacts, not new request-serving defaults.
• Temporarily fill only missing legacy WIC decisions on people explicitly identified as acs_2024_1yr with True, preserving donor and existing ACS decisions. Country-model eligibility remains unchanged.
• Validate mixed object booleans/numeric 0/1 without accepting string truthiness, missing donors, or missing identifying provenance.
• Add an obvious removal comment, replacement runbook, and focused mapping, country-engine, and CA/UT 2025–2027 preparation coverage.

Temporary assumption and follow-up

Replacement dataset publication and compatibility removal are tracked by PolicyEngine/microcosm#1154. The Microcosm code repair is PolicyEngine/microcosm#1156; rebuild/publication is performed by a separate dataset owner. The separate stacked removal draft #563 fixes #561 and must not merge before the actual replacement is published and certified. Ordinary old-name mapping remains while other certified datasets require it.

Validation

• uv run --no-sync pytest tests/test_us_legacy_inputs.py tests/test_us_legacy_inputs_integration.py -q: 87 passed.
• uv run --no-sync pytest tests/test_us_state_year_preparation.py -q: 12 passed, including complete and missing-ACS source fixtures.
• Repository formatting and current Ruff (as installed by PR CI): passed. Changed-file lint also passes with the locked local Ruff.
• Focused mypy with the local Python 3.14 environment: passed. The repository's default Python 3.11 mypy target cannot parse this environment's NumPy stubs; CI runs mypy informationally.

No full executor suite, real dataset rebuild/publication, paid compute, deployment, new environment variable, or database change.

[anth-volk]

Replaced by #566 on fix/560-temporary-acs-wic-compatibility. The replacement contains only the immediate temporary WIC compatibility fix, its focused tests, and removal instructions. The source partition/state-year preparation prototype is excluded and preserved separately on its existing branch; it must not ship with this fix. The removal follow-up #563 is being restacked on the clean compatibility branch.