fix(parallel): cover Task workflows and Responses attribution - #486

Summary

Complete the supported Python tracing paths for Parallel without expanding the Search/Extract monkeypatch.

• Add a normal application-span recipe around Task submission and result waiting, with synchronous and asynchronous examples. The span records run metadata, terminal status, request errors and local cancellation without exporting task content or raw exception text. A local wait timeout or cancellation does not imply that the remote task stopped.
• Attribute the documented api.parallel.ai Responses endpoint to parallel through the shared OpenAI instrumentor. Exact-host matching leaves proxies and lookalike domains unchanged.
• Keep existing Search/Extract entry points and their documented streaming-response scope intact. Replace the README's verification diary with runnable Task and Responses instructions.
• Add real-SDK regression coverage, loopback OTLP protobuf/JSON checks with plain/gzip transport, executable README examples, and a wheel/sdist CI matrix for minimum and current SDKs. CI runs the suites in a loopback-only network namespace.

The existing docs PR future-agi/docs#1002 should receive the matching guide after the provider mapping is released; this PR does not publish or release packages.

E2E coverage: not applicable to the product Playwright harness; SDK and exported-wire contracts cover this change.

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