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

❌ Patch coverage is 98.36066% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 98.36%. Comparing base (db89343) to head (52d37c3).
⚠️ Report is 428 commits behind head on main.

Files with missing lines	Patch %	Lines
...d_exemption/oh_homestead_exemption_total_income.py	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8310      +/-   ##
==========================================
+ Coverage   97.76%   98.36%   +0.59%     
==========================================
  Files          16        5      -11     
  Lines         269       61     -208     
  Branches        2        0       -2     
==========================================
- Hits          263       60     -203     
+ Misses          6        1       -5     

Flag	Coverage Δ
unittests	98.36% <98.36%> (+0.59%)	⬆️

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