Add API TRACE artifact builders

[MaxGhenis]

Summary

• add a TRACE artifact builder for policyengine-api simulation runs
• bind bundle, results, reform, input, request, runtime payloads, and runtime environment when policyengine.py supports the richer simulation TRO signature
• fail closed on older policyengine.py releases instead of emitting incomplete institution-backed TROs

Stack

• stacked on Migrate to policyengine v4 and resolve runtime bundles #3487
• starts Emit institutionally-signed TRACE TRO for every webapp simulation run #3485
• full runtime/request TRO emission remains blocked on Add Streamlit app for GPT4 analysis #315 being merged and released

Tests

• FLASK_DEBUG=1 uv run pytest tests/unit/libs/test_trace_artifacts.py -q
• FLASK_DEBUG=1 uv run ruff format --check policyengine_api/libs/trace_artifacts.py tests/unit/libs/test_trace_artifacts.py
• FLASK_DEBUG=1 uv run ruff check policyengine_api/libs/trace_artifacts.py tests/unit/libs/test_trace_artifacts.py

[codecov]

Codecov Report

❌ Patch coverage is 79.54545% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.62%. Comparing base (4679fed) to head (6a9aff1).

Files with missing lines	Patch %	Lines
policyengine_api/libs/trace_artifacts.py	79.54%	7 Missing and 11 partials ⚠️

Additional details and impacted files

@@                      Coverage Diff                       @@
##           migrate-to-policyengine-v4    #3509      +/-   ##
==============================================================
+ Coverage                       77.57%   77.62%   +0.04%     
==============================================================
  Files                              65       66       +1     
  Lines                            3581     3669      +88     
  Branches                          642      662      +20     
==============================================================
+ Hits                             2778     2848      +70     
- Misses                            621      628       +7     
- Partials                          182      193      +11     

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