Move all stochastic randomness to data package for deterministic country package

[baogorek]

Summary

• Remove all random() calls and seed variables from the country package
• Takeup variables (ACA, SNAP, Medicaid) are now formula-less with default_value=True
• WIC uses draw variables (wic_takeup_draw, wic_nutritional_risk_draw) instead of random()
• SSI resource test uses only actual policy logic (no more probabilistic branch)
• Add state-specific Medicaid takeup rates (53%-99% range, 51 jurisdictions)
• Add Section 1931 deprivation rules for non-expansion states (12 states)
• Add Head Start and Early Head Start takeup variables

Supersedes #6635 and #7317. Fixes #7316.

Files changed

Deleted (3 seed variables)

• aca_take_up_seed.py, snap_take_up_seed.py, medicaid_take_up_seed.py

Simplified (3 takeup variables - formula removed, default True)

• takes_up_aca_if_eligible.py, takes_up_snap_if_eligible.py, takes_up_medicaid_if_eligible.py

Created (6 new files)

• takes_up_head_start_if_eligible.py, takes_up_early_head_start_if_eligible.py
• wic_takeup_draw.py, wic_nutritional_risk_draw.py
• is_single_parent_household.py, requires_deprivation.yaml

Rewritten (3 files - no more random())

• would_claim_wic.py, is_wic_at_nutritional_risk.py, meets_ssi_resource_test.py

Updated (4 files)

• head_start.py and early_head_start.py (multiply by takeup)
• is_parent_for_medicaid_nfc.py (Section 1931 deprivation check)
• takeup_rate.yaml (state-specific Medicaid rates)

Test plan

• WIC tests: 42 passed
• Medicaid tests: 145 passed
• SNAP tests: 205 passed
• SSI tests: 132 passed
• ACA + Head Start tests: 150 passed
• No random() calls remain in any variable file
• Black formatting passes
• Full test suite

Merge order

PolicyEngine/policyengine-us-data#451 must be merged FIRST, then this PR.

Related

• Data package companion: Move all randomness to data package for deterministic country package policyengine-us-data#451
• Original PRs superseded: Make country package purely deterministic - read stochastic variables from dataset #6635, Add state-specific Medicaid takeup rates and Section 1931 deprivation rules #7317
• UK pattern: Make country package purely deterministic - read stochastic variables from dataset policyengine-uk#1355, Move all randomness to data package for deterministic country package policyengine-uk-data#203

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.56%. Comparing base (901599b) to head (a46b5a8).
⚠️ Report is 31 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/variables/gov/hhs/head_start/early_head_start.py	0.00%	2 Missing ⚠️
...gine_us/variables/gov/hhs/head_start/head_start.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##              main    #7326       +/-   ##
============================================
- Coverage   100.00%   86.56%   -13.44%     
============================================
  Files            3       12        +9     
  Lines           54      134       +80     
  Branches         1        0        -1     
============================================
+ Hits            54      116       +62     
- Misses           0       18       +18     

Flag	Coverage Δ
unittests	86.56% <91.66%> (-13.44%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[MaxGhenis]

All test suites pass. Codecov failures are non-blocking (Head Start takeup multiplication lines). Takeup parameters cleaned up — now exclusively in us-data.