Add CHIP enrollment calibration targets

[daphnehanse11]

Starts PolicyEngine/policyengine-us#8523 by adding CHIP enrollment controls and take-up plumbing for CPS/data calibration.\n\nSummary:\n- add 2024-2026 state CHIP enrollment target CSVs from CMS Total CHIP Enrollment\n- add CHIP enrollment targets to legacy loss.py and structured target config/ETL\n- wire takes_up_chip_if_eligible through CPS, local H5, entity clone, and unified matrix take-up paths with the current full-takeup default\n- anchor CHIP take-up to CPS NOW_PCHIP reports where available\n\nTests:\n- uv run ruff check policyengine_us_data/datasets/cps/cps.py policyengine_us_data/db/etl_medicaid.py policyengine_us_data/utils/loss.py policyengine_us_data/utils/takeup.py policyengine_us_data/build_outputs/us_augmentations.py policyengine_us_data/calibration/entity_clone.py policyengine_us_data/calibration/unified_matrix_builder.py tests/integration/test_cps_generation.py tests/unit/build_outputs/test_us_augmentations.py tests/unit/calibration/test_loss_targets.py tests/unit/calibration/test_target_config.py tests/unit/calibration/test_unified_calibration.py tests/unit/test_etl_medicaid.py\n- uv run ruff format --check policyengine_us_data/datasets/cps/cps.py policyengine_us_data/db/etl_medicaid.py policyengine_us_data/utils/loss.py policyengine_us_data/utils/takeup.py policyengine_us_data/build_outputs/us_augmentations.py policyengine_us_data/calibration/entity_clone.py policyengine_us_data/calibration/unified_matrix_builder.py tests/integration/test_cps_generation.py tests/unit/build_outputs/test_us_augmentations.py tests/unit/calibration/test_loss_targets.py tests/unit/calibration/test_target_config.py tests/unit/calibration/test_unified_calibration.py tests/unit/test_etl_medicaid.py\n- uv run pytest tests/unit/calibration/test_loss_targets.py::test_chip_targets_roll_forward_to_2026 tests/unit/calibration/test_loss_targets.py::test_chip_targets_fall_back_to_earliest_available_year tests/unit/calibration/test_loss_targets.py::test_chip_national_target_uses_2026_enrollment tests/unit/build_outputs/test_us_augmentations.py::test_build_reported_takeup_anchors_uses_present_period tests/unit/calibration/test_target_config.py::TestLoadTargetConfig::test_training_config_uses_enrollment_flag_for_medicaid_count_target tests/integration/test_cps_generation.py::test_add_takeup_removes_temporary_source_anchors_from_saved_h5 tests/unit/test_etl_medicaid.py tests/unit/calibration/test_unified_calibration.py::TestSimpleTakeupConfig tests/unit/calibration/test_unified_calibration.py::TestTakeupAffectedTargets

[daphnehanse11]

Closing as superseded by the Populace migration. Populace now owns the US calibration target surface and already includes CMS Medicaid and Medicaid+CHIP combined enrollment targets.

Remaining follow-up: Populace should add/diagnose direct CHIP enrollment targets or otherwise improve the Medicaid/CHIP split. The old policyengine-us-data implementation here is stale/conflicting and should not be the place we continue that work.