Ignore deprecated medical expense input

[MaxGhenis]

Summary

• Add a standard API deprecated-input scrubber for medical_out_of_pocket_expenses.
• Strip that removed variable before household calculations reach the engine.
• Return warning strings on successful responses when deprecated inputs are ignored.

Context

MFB falls back from household.api.policyengine.org/us/calculate to api.policyengine.org/us/calculate when household API requests time out. Household API already ignores medical_out_of_pocket_expenses and returns a warning, but the standard API fallback still returns a fast HTTP 500 for payloads containing the removed field.

This applies the same graceful behavior to standard API household calculations so MFB fallback requests can keep computing while they migrate to other_medical_expenses and health_insurance_premiums.

Testing

• uv run pytest tests/test_deprecated_inputs.py -q
• uv run ruff check policyengine_api/endpoints/household.py policyengine_api/utils/deprecated_inputs.py tests/test_deprecated_inputs.py

[codecov]

Codecov Report

❌ Patch coverage is 21.11111% with 71 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.58%. Comparing base (1fd9618) to head (5f2eac2).
⚠️ Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
policyengine_api/utils/deprecated_inputs.py	24.00%	57 Missing ⚠️
policyengine_api/endpoints/household.py	6.66%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3574      +/-   ##
==========================================
- Coverage   77.81%   76.58%   -1.24%     
==========================================
  Files          65       66       +1     
  Lines        3877     3968      +91     
  Branches      697      724      +27     
==========================================
+ Hits         3017     3039      +22     
- Misses        683      752      +69     
  Partials      177      177              

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[MaxGhenis]

Closing in favor of #3576, which now includes the deprecated medical expense input fallback plus structured 400 responses for unrecognized calculate inputs.