Summary

• Adds South Carolina's Homestead Exemption for senior, disabled, and blind homeowners.
• Models the exemption for the first $50,000 of fair market residence value, converted to a $2,000 assessed-value exemption using South Carolina's 4% legal-residence assessment rate.
• Adds focused eligibility, exemption, and reduction tests.

Closes #8201.

Value Review

• South Carolina Department of Revenue says the Homestead Exemption exempts the first $50,000 of the fair market value of the dwelling place for qualifying homeowners.
• The same source states legal residences are assessed at 4%, so this PR applies the $50,000 exemption as $2,000 of assessed value before estimating the property-tax reduction.

Source:

• South Carolina Department of Revenue, Exempt Property: https://dor.sc.gov/property/exempt-property

Tests

• uv run policyengine-core test policyengine_us/tests/policy/baseline/gov/states/sc/tax/property/homestead_exemption -c policyengine_us
• uv run pytest policyengine_us/tests/test_parameter_files.py policyengine_us/tests/test_system_import.py -q
• uv run --extra dev ruff check policyengine_us/variables/gov/states/sc/tax/property/homestead_exemption