Fix OpenInference trace patch lifecycle

[tconley1428]

Summary

• scope the OpenInference trace-start patch to active OpenAI Agents tracing contexts
• prevent nested wrappers when multiple contexts are active
• restore the original method after the final context exits
• add a regression test for the patch lifecycle

Why

The patch previously remained installed after instrumentation was removed. Each new OTel-enabled AgentEnvironment wrapped the previous patch, causing suite-order-dependent context work during workflow replay.

Validation

• uv sync --all-extras
• poe build-develop
• poe test -s -k 'otel_trace_start_patch_does_not_nest or test_sdk_trace_to_otel_span_parenting'
• poe lint (Ruff and Pyright passed; the Mypy step did not return a final status before the command session ended)