feat(streaming): emit OTel metrics for ttft, tps, token counts #1501

Job	Run time
find-tutorials	4s
test-00_sync/020_streaming	2m 32s
test-10_async/00_base/080_batch_events	2m 46s
test-00_sync/010_multiturn	2m 24s
test-10_async/00_base/010_multiturn	2m 46s
test-10_async/00_base/000_hello_acp	1m 56s
test-00_sync/000_hello_acp	2m 2s
test-10_async/00_base/100_langgraph	2m 14s
test-10_async/00_base/020_streaming	2m 10s
test-10_async/10_temporal/010_agent_chat	2m 38s
test-00_sync/030_langgraph	2m 57s
test-10_async/10_temporal/070_open_ai_agents_sdk_tools	2m 4s
test-10_async/10_temporal/090_claude_agents_sdk_mvp	1m 54s
test-10_async/10_temporal/000_hello_acp	2m 39s
test-10_async/10_temporal/030_custom_activities	1m 52s
test-10_async/10_temporal/020_state_machine	2m 16s
test-10_async/00_base/030_tracing	1m 58s
test-10_async/10_temporal/050_agent_chat_guardrails	1m 54s
test-10_async/00_base/040_other_sdks	3m 43s
test-10_async/10_temporal/080_open_ai_agents_sdk_human_in_the_loop	2m 6s
test-10_async/10_temporal/060_open_ai_agents_sdk_hello_world	1m 57s
Test Summary	5s
	46m 57s

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