feat(streaming): emit OTel metrics for ttft, tps, token counts #1499

Job	Run time
find-tutorials	5s
test-00_sync/030_langgraph	3m 42s
test-10_async/00_base/020_streaming	2m 3s
test-10_async/00_base/010_multiturn	2m 8s
test-10_async/00_base/030_tracing	2m 5s
test-00_sync/020_streaming	2m 38s
test-00_sync/000_hello_acp	2m 23s
test-10_async/10_temporal/000_hello_acp	2m 4s
test-10_async/00_base/100_langgraph	2m 1s
test-00_sync/010_multiturn	2m 57s
test-10_async/00_base/040_other_sdks	3m 53s
test-10_async/10_temporal/070_open_ai_agents_sdk_tools	1m 59s
test-10_async/10_temporal/050_agent_chat_guardrails	1m 54s
test-10_async/00_base/000_hello_acp	2m 55s
test-10_async/10_temporal/010_agent_chat	8m 25s
test-10_async/10_temporal/020_state_machine	2m 21s
test-10_async/10_temporal/030_custom_activities	2m 1s
test-10_async/10_temporal/060_open_ai_agents_sdk_hello_world	1m 55s
test-10_async/10_temporal/090_claude_agents_sdk_mvp	1m 56s
test-10_async/00_base/080_batch_events	3m 10s
test-10_async/10_temporal/080_open_ai_agents_sdk_human_in_the_loop	1m 58s
Test Summary	4s
	54m 37s

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