Add person_receives_aca and assigned ACA PTC variables

[daphnehanse11]

Closes #7806

Summary

• add person_receives_aca as a person-level ACA receipt flag
• keep aca_ptc as the pre-takeup ACA premium tax credit amount and add assigned_aca_ptc for the amount actually assigned after take-up
• add YAML coverage for base ACA PTC behavior, assigned ACA PTC behavior, and person-level ACA receipt

Testing

• make format
• uv run policyengine-core test policyengine_us/tests/policy/baseline/gov/aca/ptc/aca_ptc.yaml policyengine_us/tests/policy/baseline/gov/aca/ptc/assigned_aca_ptc.yaml policyengine_us/tests/policy/baseline/gov/aca/person_receives_aca.yaml -c policyengine_us

[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.89%. Comparing base (fd8a1f8) to head (932f195).
⚠️ Report is 122 commits behind head on main.

Files with missing lines	Patch %	Lines
...les/household/income/spm_unit/spm_unit_benefits.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main    #7808      +/-   ##
===========================================
- Coverage   100.00%   91.89%   -8.11%     
===========================================
  Files           12        7       -5     
  Lines          174       74     -100     
  Branches         0        2       +2     
===========================================
- Hits           174       68     -106     
- Misses           0        6       +6     

Flag	Coverage Δ
unittests	91.89% <95.65%> (-8.11%)	⬇️

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[PavelMakarchuk]

Review: Downstream breakage from removing takeup gate on aca_ptc

The core change — separating aca_ptc (potential) from assigned_aca_ptc (post-takeup) — is a good design. But removing the takeup gate from aca_ptc without updating downstream references is a breaking change.

Problem

4 files reference aca_ptc and expect it to be the actual credit received (post-takeup):

File	Usage	Impact if aca_ptc becomes pre-takeup
spm_unit_benefits.py	BENEFITS.append("aca_ptc")	Non-taken-up PTC counted as benefits
healthcare_benefit_value.py	Lists aca_ptc	Overstates healthcare benefit value
premium_tax_credit.py	adds = ["aca_ptc"]	Flows into federal tax computation
income_tax_excluding_ptc.py	subtracts = ["aca_ptc"]	Understates tax excluding PTC

These would cause household_net_income, spm_unit_benefits, and federal tax calculations to be wrong for anyone who doesn't take up ACA.

Fix

These 4 references should switch from aca_ptc to assigned_aca_ptc:

# spm_unit_benefits.py
BENEFITS.append("assigned_aca_ptc")  # was "aca_ptc"

# healthcare_benefit_value.py
"assigned_aca_ptc",  # was "aca_ptc"

# premium_tax_credit.py
adds = ["assigned_aca_ptc"]  # was ["aca_ptc"]

# income_tax_excluding_ptc.py
subtracts = ["assigned_aca_ptc"]  # was ["aca_ptc"]

CI failure

The Full Suite - Baseline (excl States) failure is a pre-existing hourly_wage data array mismatch in the microsim test — not caused by this PR.

Other notes

• The new variables and tests look clean
• person_receives_aca logic is correct (person eligible AND tax unit takes up)
• Test case 5 (takeup counts even when assigned PTC is $0) is a good edge case
• The aca_ptc test confirming it's available even without takeup correctly validates the new semantics

[PavelMakarchuk]

Question on benefit accounting