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.

Closes #8200.

Tests

• /Users/daphnehansell/Documents/GitHub/policyengine-us/.venv/bin/python policyengine_us/tests/test_batched.py policyengine_us/tests/policy/baseline/gov/states/oh/tax/property/homestead_exemption --batches 1
• /Users/daphnehansell/Documents/GitHub/policyengine-us/.venv/bin/ruff check policyengine_us/variables/gov/states/oh/tax/property/homestead_exemption
• /Users/daphnehansell/Documents/GitHub/policyengine-us/.venv/bin/python -m pytest policyengine_us/tests/test_parameter_files.py policyengine_us/tests/test_system_import.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (8cb60e7) to head (9e251e4).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #8310   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            3         3           
  Lines           63        41   -22     
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- Hits            63        41   -22     

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

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