Fix asset stock period handling

[MaxGhenis]

Summary

• Mark household asset, property value, SNAP asset, Pell asset, and selected state asset variables as stock quantities so monthly formulas do not divide balances by 12.
• Remove an Illinois AABD vehicle-value workaround that multiplied a vehicle stock by 12.
• Model Texas SNAP BBCE excess vehicle value in the TANF non-cash asset test and remove the stale "not modeled" note.
• Periodize the Texas vehicle exemption at $15,000 before September 1, 2023 and $22,500 afterward, citing Texas HB 1287 and the Texas Works Handbook.
• Add regression coverage for SNAP asset stocks and Texas BBCE vehicle assets.

Fixes #8300.

Context

PolicyBench error review found cases where SNAP categorical eligibility used monthly TANF non-cash asset tests. Because asset balances were treated as annual flows, a $15,000 asset balance appeared as $1,250 in monthly formulas and could incorrectly pass state asset tests.

The same review also surfaced a separate Texas SNAP BBCE gap: PE-US documented that excess vehicle value above the Texas vehicle exemption was not modeled for the TANF non-cash asset test used by SNAP BBCE. This PR models excess vehicle value using household vehicle value and the Texas exemption. The current Texas exemption is $22,500 for the first vehicle under HB 1287, effective September 1, 2023; $15,000 remains as the historical pre-HB 1287 value.

PolicyEngine Core already preserves stock quantities across periods when variables declare quantity_type = STOCK, so the period-handling fix is in PE-US rather than core.

Related PolicyBench prompt follow-up: PolicyEngine/policybench#19.

Tests

• uv run policyengine-core test policyengine_us/tests/policy/baseline/gov/hhs/tanf/non_cash/meets_tanf_non_cash_asset_test.yaml policyengine_us/tests/policy/baseline/gov/usda/snap/eligibility/snap_assets.yaml -c policyengine_us
• uv run --frozen python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/gov/hhs/tanf/non_cash policyengine_us/tests/policy/baseline/gov/usda/snap/eligibility -c policyengine_us
• uv run --frozen python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/gov/states/dc/dhs/ccsp/eligibility/dc_ccsp_asset_eligible.yaml policyengine_us/tests/policy/baseline/gov/states/il/dhs/aabd/asset/il_aabd_asset_value_eligible.yaml policyengine_us/tests/policy/baseline/gov/states/il/dhs/aabd/asset/il_aabd_countable_vehicle_value.yaml policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/asset/il_hbwd_countable_assets.yaml policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/eligibility/il_hbwd_asset_eligible.yaml policyengine_us/tests/policy/baseline/gov/states/ma/dta/tcap/eaedc/eligibility/financial/ma_eaedc_assets_limit_eligible.yaml policyengine_us/tests/policy/baseline/gov/states/ma/eec/ccfa/eligibility/ma_ccfa_asset_eligible.yaml -c policyengine_us
• uv run --frozen python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/gov/states/tn/dhs/ff/tn_ff_countable_resources.yaml policyengine_us/tests/policy/baseline/gov/states/wa/dshs/tanf/wa_tanf_countable_resources.yaml policyengine_us/tests/policy/baseline/gov/states/tx/tanf/resources/tx_tanf_countable_resources.yaml policyengine_us/tests/policy/baseline/gov/states/wi/dcf/works/wi_works_countable_resources.yaml policyengine_us/tests/policy/baseline/gov/local/ca/la/general_relief/eligible/la_general_relief_motor_vehicle_value_eligible.yaml policyengine_us/tests/policy/baseline/gov/local/ca/riv/general_relief/ca_riv_general_relief_countable_vehicle_value.yaml policyengine_us/tests/policy/baseline/gov/states/ca/cdss/tanf/cash/eligibility/ca_tanf_vehicle_value_eligible.yaml policyengine_us/tests/policy/baseline/gov/states/ca/cdss/capi/resources/ca_capi_countable_vehicle_value.yaml policyengine_us/tests/policy/baseline/gov/states/ca/cdss/capi/resources/ca_capi_resources.yaml policyengine_us/tests/policy/baseline/gov/states/mt/dhs/tanf/eligibility/mt_tanf_countable_resources.yaml policyengine_us/tests/policy/baseline/gov/states/nm/hca/nm_works/resources/nm_works_countable_non_liquid_resources.yaml policyengine_us/tests/policy/baseline/gov/states/nm/hca/nm_works/resources/nm_works_countable_resources.yaml policyengine_us/tests/policy/baseline/gov/states/dc/dhs/tanf/eligibility/dc_tanf_countable_resources.yaml policyengine_us/tests/policy/baseline/gov/states/in/fssa/tanf/resources/in_tanf_countable_resources.yaml -c policyengine_us
• uv run --frozen python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/gov/local/ca/ala/eligibility/ca_ala_general_assistance_personal_property_eligible.yaml policyengine_us/tests/policy/baseline/gov/local/ca/la/general_relief/eligible/la_general_relief_personal_property_eligible.yaml policyengine_us/tests/policy/baseline/gov/local/ca/la/general_relief/eligible/la_general_relief_home_value_eligible.yaml policyengine_us/tests/policy/baseline/gov/states/wa/dshs/tanf/wa_tanf_countable_resources.yaml policyengine_us/tests/policy/baseline/gov/states/wv/tax/income/credits/sctc/wv_sctc.yaml policyengine_us/tests/policy/baseline/gov/states/wv/tax/income/exemptions/homestead_exemption/wv_homestead_exemption.yaml policyengine_us/tests/policy/baseline/gov/irs/integration/qbid.yaml policyengine_us/tests/policy/baseline/gov/irs/income/taxable_income/deductions/qualified_business_income_deduction_person.yaml policyengine_us/tests/policy/baseline/gov/irs/tax/estate/estate_tax.yaml policyengine_us/tests/policy/baseline/gov/irs/tax/estate/estate_tax_before_credits.yaml policyengine_us/tests/policy/baseline/gov/irs/credits/estate/estate_tax_credit.yaml -c policyengine_us
• uv run --frozen ruff format --check
• uv run --frozen ruff check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.56%. Comparing base (8cb60e7) to head (efc0af4).
⚠️ Report is 21 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##              main    #8298      +/-   ##
===========================================
- Coverage   100.00%   97.56%   -2.44%     
===========================================
  Files            3       38      +35     
  Lines           63      452     +389     
  Branches         0        3       +3     
===========================================
+ Hits            63      441     +378     
- Misses           0       10      +10     
- Partials         0        1       +1     

Flag	Coverage Δ
unittests	97.56% <100.00%> (-2.44%)	⬇️

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