refactor(harness): move OpenAI harness into adk/_modules + facade export #1821

Job	Run time
find-tutorials	6s
test-00_sync/040_pydantic_ai	2m 19s
test-00_sync/010_multiturn	2m 41s
test-00_sync/050_openai_agents	2m 21s
test-10_async/00_base/110_pydantic_ai	2m 11s
test-00_sync/030_langgraph	3m 9s
test-10_async/00_base/020_streaming	2m 13s
test-10_async/00_base/010_multiturn	2m 26s
test-00_sync/000_hello_acp	1m 59s
test-10_async/00_base/030_tracing	2m 1s
test-00_sync/020_streaming	2m 51s
test-00_sync/070_codex	2m 48s
test-10_async/10_temporal/030_custom_activities	1m 56s
test-00_sync/060_claude_code	2m 26s
test-10_async/00_base/100_langgraph	2m 27s
test-10_async/10_temporal/050_agent_chat_guardrails	2m 1s
test-10_async/00_base/140_codex	2m 16s
test-10_async/00_base/130_claude_code	2m 22s
test-10_async/00_base/000_hello_acp	2m 6s
test-10_async/10_temporal/020_state_machine	2m 23s
test-10_async/10_temporal/010_agent_chat	4m 14s
test-10_async/10_temporal/060_open_ai_agents_sdk_hello_world	2m 8s
test-10_async/10_temporal/110_pydantic_ai	2m 4s
test-10_async/00_base/080_batch_events	3m 18s
test-10_async/10_temporal/120_openai_agents	2m 9s
test-10_async/10_temporal/090_claude_agents_sdk_mvp	2m 12s
test-10_async/10_temporal/070_open_ai_agents_sdk_tools	2m 24s
test-10_async/00_base/120_openai_agents	2m 21s
test-10_async/10_temporal/000_hello_acp	2m 8s
test-10_async/00_base/040_other_sdks	3m 48s
test-10_async/10_temporal/080_open_ai_agents_sdk_human_in_the_loop	2m 14s
test-10_async/10_temporal/130_langgraph	2m 9s
test-10_async/10_temporal/140_claude_code	2m 38s
test-10_async/10_temporal/150_codex	2m 24s
Test Summary	6s
	1h 21m 19s

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