Remove US-data Medicaid cost allocator

[daphnehanse11]

Summary

Removes the duplicate Medicaid conditional-cost allocator from policyengine-us-data so Medicaid cost logic can live in PolicyEngine US.

• removes the CPS and Extended CPS Medicaid cost generation hooks
• deletes the us-data SLCSP allocator and its tests
• removes the local H5 Medicaid cost postprocessor and associated tests
• regenerates pipeline docs after removing the postprocessor node
• pins policyengine-us==1.715.2, the released PE-US version containing the formula-backed medicaid_cost_if_enrolled variable
• adds a dependency contract test so us-data fails fast if the pinned PE-US package does not provide the Medicaid cost formula

Depends on PolicyEngine/policyengine-us#8538, which has been merged and released as policyengine-us==1.715.2.

Tests

• uv run ruff format tests/unit/test_policyengine_us_dependency_contract.py --check
• uv run ruff check tests/unit/test_policyengine_us_dependency_contract.py
• env -u UV_FROZEN uv lock --check
• uv run pytest tests/unit/test_policyengine_us_dependency_contract.py tests/unit/build_outputs/test_us_augmentations.py tests/unit/calibration/test_publish_local_area.py tests/unit/test_pipeline_docs_extractor.py

[MaxGhenis]

Fixed the release sequencing issue from review.

• Merged Move Medicaid cost allocation into PE-US policyengine-us#8538 and waited for policyengine-us==1.715.2 to publish.
• Updated us-data to pin policyengine-us==1.715.2 and refreshed uv.lock.
• Added a dependency contract test asserting medicaid_cost_if_enrolled is formula-backed in the pinned PE-US package.

Local verification:

• uv run pytest tests/unit/test_policyengine_us_dependency_contract.py tests/unit/build_outputs/test_us_augmentations.py tests/unit/calibration/test_publish_local_area.py tests/unit/test_pipeline_docs_extractor.py
• uv run ruff format tests/unit/test_policyengine_us_dependency_contract.py --check
• uv run ruff check tests/unit/test_policyengine_us_dependency_contract.py
• env -u UV_FROZEN uv lock --check

[MaxGhenis]

Reviewed the Medicaid cost allocator removal after PE-US 1.715.2 release. CI is green and the dependency contract now guards the formula-backed medicaid_cost_if_enrolled requirement.