fix(examples-py): validate LiveKit, LlamaIndex, and Marqo OTel 2.x spans

[Nightingalelyy]

Summary

• add a bounded live LiveKit OpenAI-plugin example through the configured Respan gateway while keeping the deterministic stream/tool/error scenarios
• preserve one exact RESPAN_EXAMPLE_RUN_ID, provider context, and guaranteed cleanup across all LiveKit examples
• make every LlamaIndex example preserve the invocation marker, shut down explicitly, and give the query root bounded request/answer content
• run the real Marqo 3.18 client against an ephemeral protocol fixture for deterministic success and 503 failure coverage, with an opt-in configured service path

Validation

• LiveKit examples: 5/5 passed
• LlamaIndex examples: 5/5 passed
• Marqo examples: 2/2 passed
• shared marker otel2-fix-py-group-17-20260817T111735Z: 12 traces / 58 full records inspected through Respan MCP
• final LiveKit marker otel2-fix-py-group-17-livekit-clean-20260817T112900Z: 5 traces / 7 full records, one root per tree, no orphan/duplicate spans, exact usage/content/provider/stream fields
• Ruff check and format-check passed for every changed Python example file

Companion instrumentation: respanai/respan#383