Construct CPS tax units from household records

[MaxGhenis]

Summary

Builds CPS tax units from ASEC household records instead of using Census TAX_ID as the production tax-unit graph.

Key points:

• Constructs tax units from reciprocal spouses, parent pointers, student/disability/age eligibility, gross-income limits, and relationship rules.
• Keeps only constructed TAX_IDs in the staged CPS data path; PE-US infers tax-unit roles and filing statuses from the resulting graph.
• Preserves CENSUS_TAX_ID for audit/comparison.
• Adds a census_documented comparison mode and two validation harnesses.
• Adds unit and integration coverage for assignment edge cases and CPS staging.

Closes #815.

Validation

Structural comparison against the 2025 ASEC public person file for tax year 2024:

• Household exact match vs Census: 93.55%
• Exact match excluding Census spouse-split households: 96.91%
• Person same-unit match: 92.97%
• Reciprocal spouse splits: Census 6.82%, constructed 0.00%
• Qualifying-child parent-pointer splits: Census 1.86%, constructed 0.34%
• Minor singleton rate: Census 1.35%, constructed 1.28%

Outcome comparison holding staged CPS arrays fixed and swapping only tax-unit IDs:

• Taxable SOI rows mean absolute relative error: 1.12884 -> 1.12773
• Selected tax rows mean absolute relative error: 0.68472 -> 0.67852
• Selected tax rows RMSE relative error: 2.45406 -> 2.40138
• Aggregate SOI rows mean absolute relative error: 1.17441 -> 1.17380

Commands run:

• uv run ruff check policyengine_us_data/datasets/cps/census_cps.py policyengine_us_data/datasets/cps/cps.py policyengine_us_data/datasets/cps/tax_unit_construction.py policyengine_us_data/datasets/cps/tax_unit_rule_helpers.py tests/integration/test_census_cps.py tests/integration/test_cps.py tests/unit/datasets/test_cps_tax_unit_construction.py validation/cps_tax_unit_validation.py validation/cps_tax_unit_outcome_validation.py
• uv run pytest tests/unit/datasets/test_cps_tax_unit_construction.py -q
• uv run pytest tests/integration/test_census_cps.py -k 'resolve_person_usecols or fill_missing_optional_person_columns or create_tax_unit_table' -q
• uv run pytest tests/integration/test_cps.py -k 'add_personal_variables or add_id_variables or validate_raw_cps_schema' -q
• PYTHONPATH=/Users/maxghenis/PolicyEngine/policyengine-us uv run python validation/cps_tax_unit_outcome_validation.py policyengine_us_data/storage/cps_2024.h5 /tmp/asecpub25csv.zip --csv-name pppub25.csv --year 2024 --output /tmp/cps_tax_unit_outcome_validation_ids_only.json