Split candidate staging versions

[anth-volk]

Fixes #972

Summary

• Split candidate staging paths from final release versions so staged artifacts are scoped by candidate version and run ID.
• Keep final release records tied to the release version.
• Temporarily skip the Stage 1 Medicaid enrollment validator with a dedicated pytest marker while Confirm Medicaid Stage 1 validator year alignment #971 confirms whether the 2024 target / 2025 formula-period alignment is intentional.

Testing

• make lint
• uv run --no-sync --with pytest --with sqlalchemy --with sqlmodel --with policyengine-us==1.691.3 python -m pytest validation/stage_1/test_enhanced_cps.py::test_medicaid_calibration -q

Related: #971