Replace high-value surcharge test with YAML policy tests

[MaxGhenis]

Summary

• replace the bespoke test_high_value_council_tax_surcharge.py test with standard YAML policy tests
• cover the same behavior from #1568: 2028 start date, 2029 uprating, aggregate flow into household_tax/gov_tax, and England-only scope
• override gov.hmrc.stamp_duty.property_sale_rate in the YAML cases so the aggregate assertions stay stable

Testing

• uv run policyengine-core test policyengine_uk/tests/policy/baseline/gov/hmrc/council_tax/high_value_council_tax_surcharge.yaml -c policyengine_uk
• uv run python -m pytest -q policyengine_uk/tests