Add remaining eCPS take-up inputs

[MaxGhenis]

Summary

• add eCPS-style deterministic take-up inputs for Medicaid, TANF, DC PTC, Head Start, Early Head Start, EITC, and voluntary filing
• preserve explicit source take-up flags when present, including tax-unit flags carried on person rows
• prefer imputed eitc_children for EITC take-up rates when available, falling back to reconstructed tax-unit dependent counts
• load latest eCPS voluntary-filing rates as the nested child/wage/age table rather than the older scalar fallback

Notes

This intentionally does not copy eCPS WIC or SSI behavior. WIC needs coherent category/risk source modeling, and SSI already has MP's reported/calibrated take-up path.

Validation

• uv run ruff check src/microplex_us/pipelines/us.py tests/pipelines/test_us.py
• uv run ruff format --check src/microplex_us/pipelines/us.py tests/pipelines/test_us.py
• uv run --extra dev python -m pytest tests/pipelines/test_us.py -q -k 'adds_ecps_stochastic_takeup_inputs or preserves_explicit_stochastic_takeup_inputs or uses_eitc_children_for_eitc_takeup or adds_deterministic_snap_takeup or adds_deterministic_aca_takeup'
• PYTHONPATH=/Users/maxghenis/.codex-worktrees/policyengine-us-data-upstream-main-20260601 uv run --extra policyengine python - <<'PY' ... verified the 2024 voluntary-filing loader returns the nested no_children/with_children table shape

Full local test_us.py was not run before opening because the machine is already running the active MP H5 build and several Claude pytest jobs; CI should cover the broader suite.