reuse sessions to eliminate fd leak

[xzrderek]

Note

Summary
Improves HTTP resource management to prevent FD leaks by reusing sessions and ensuring responses are closed.

• Use a shared requests.Session in FireworksTracingAdapter and RemoteRolloutProcessor; wrap all GET/POST calls in context managers to auto-close responses
• Add FireworksTracingAdapter.close() and call it from RemoteRolloutProcessor.cleanup(); also close the processor's own session in cleanup
• Refine error handling in get_evaluation_rows to parse detail from proxy JSON and log precise messages
• Minor adjustments to /logs retrieval with fallback and normalized results

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