Add Pennsylvania property tax/rent rebate

[daphnehanse11]

Summary

• Adds Pennsylvania's standard Property Tax/Rent Rebate eligibility and 2025 PA-1000 income-based rebate table: $1,000 / $770 / $460 / $380 through the $48,110 income limit.
• Models PA-1000 rebate income instead of plain federal AGI, including half-counted Social Security, reported SSI, and railroad benefits, and adding available tax-exempt interest and retirement income.
• Caps homeowner rebates by property tax paid and renter rebates by 20% of eligible rent paid, with the combined owner/renter amount still capped by the standard rebate table.
• Models senior/spouse, widow(er), and disabled-adult eligibility, including a widowed filer marker outside federal surviving-spouse filing status.

Closes #8181.

Limitations

• This PR models the standard rebate table and leaves supplemental rebates for follow-up.
• This PR does not model PA-1000 schedule adjustments for partial-year/decedent claims, remarried widow(er)s, public-assistance rent reductions, business use of the residence, shared ownership/leases, annualized-income alternatives, or tax-exempt landlord/PILOT renter restrictions.
• PA-1000-only income sources that are not represented by available model inputs remain out of scope.

Tests

• uv run --with ruff ruff format --check policyengine_us/variables/gov/states/pa/tax/property/property_tax_or_rent_rebate/pa_property_tax_or_rent_rebate.py policyengine_us/variables/gov/states/pa/tax/property/property_tax_or_rent_rebate/pa_property_tax_or_rent_rebate_eligible.py policyengine_us/variables/gov/states/pa/tax/property/property_tax_or_rent_rebate/pa_property_tax_or_rent_rebate_income.py
• uv run python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/gov/states/pa/tax/property/property_tax_or_rent_rebate -c policyengine_us
• uv run python -m pytest policyengine_us/tests/test_parameter_files.py -q

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (8cb60e7) to head (e0ef9c8).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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- Hits            63        57    -6     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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