feat: stamp gateway attribution metadata

[haasonsaas]

Summary

• add team, workload, session, and evidence attribution headers to the OpenAI shim
• pass the new attribution options through sync and async Python clients and the TypeScript client
• keep org/principal/trace behavior backward compatible

Tests

• npm test
• npm run typecheck
• .venv/bin/python -m pytest tests

[cursor]

PR Summary

Low Risk
Low risk: adds optional request headers and plumbs new constructor options/env vars through the OpenAI shims without changing existing org/principal/trace behavior.

Overview
Adds support for stamping additional gateway attribution metadata (team, workload, session, evidence) as X-EvalOps-* headers in both the Python and TypeScript OpenAI shims.

Plumbs the new options through OpenAI/AsyncOpenAI (Python) and EvalOpsOpenAI (TS), resolving values from explicit options or EVALOPS_* env vars, and updates unit tests to assert the new headers.

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