Add Ohio homestead property tax exemption

[daphnehanse11]

Summary

• Adds Ohio's Homestead Exemption for senior, disabled, and qualifying surviving-spouse homeowners.
• Adds 2025 and 2026 indexed exemption amounts and the income limit parameter.
• Models the exempt assessed value and the corresponding property-tax reduction.
• Keeps the rule household-calculator-only for now; this PR does not wire the reduction into baseline property-tax-credit aggregates while assessed-property-value data readiness is unresolved.

Closes #8200.

Tests

• PYTHONPATH=. /Users/daphnehansell/Documents/GitHub/policyengine-us/.venv/bin/python -m policyengine_core.scripts.policyengine_command test policyengine_us/tests/policy/baseline/gov/states/oh/tax/property/homestead_exemption -c policyengine_us
• /Users/daphnehansell/Documents/GitHub/policyengine-us/.venv/bin/ruff check policyengine_us/variables/gov/states/oh/tax/property/homestead_exemption

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (eee0f91) to head (5c622d7).
⚠️ Report is 128 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##             main     #8310       +/-   ##
============================================
+ Coverage   78.72%   100.00%   +21.27%     
============================================
  Files        4723         3     -4720     
  Lines       68774        41    -68733     
  Branches      340         0      -340     
============================================
- Hits        54142        41    -54101     
+ Misses      14554         0    -14554     
+ Partials       78         0       -78     

Flag	Coverage Δ
unittests	100.00% <100.00%> (+21.27%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.