feat(streaming): emit OTel metrics for ttft, tps, token counts #1500

Job	Run time
find-tutorials	3s
test-00_sync/020_streaming	2m 30s
test-10_async/00_base/030_tracing	2m 3s
test-10_async/10_temporal/000_hello_acp	2m 6s
test-10_async/10_temporal/010_agent_chat	2m 50s
test-10_async/00_base/020_streaming	1m 58s
test-00_sync/000_hello_acp	2m 2s
test-10_async/00_base/040_other_sdks	3m 17s
test-00_sync/010_multiturn	2m 18s
test-10_async/10_temporal/090_claude_agents_sdk_mvp	3m 19s
test-10_async/00_base/080_batch_events	2m 51s
test-10_async/00_base/010_multiturn	2m 4s
test-10_async/00_base/100_langgraph	2m 7s
test-10_async/00_base/000_hello_acp	1m 57s
test-00_sync/030_langgraph	2m 51s
test-10_async/10_temporal/020_state_machine	2m 18s
test-10_async/10_temporal/080_open_ai_agents_sdk_human_in_the_loop	1m 57s
test-10_async/10_temporal/060_open_ai_agents_sdk_hello_world	1m 57s
test-10_async/10_temporal/070_open_ai_agents_sdk_tools	1m 56s
test-10_async/10_temporal/050_agent_chat_guardrails	2m 8s
test-10_async/10_temporal/030_custom_activities	2m 1s
Test Summary	3s
	46m 36s

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