Add a sandbox sample and snipsync markers for the OpenAI Agents docs guide #1380

Job	Run time
build-lint-test (3.10, macos-arm)	8m 34s
build-lint-test (3.14, windows-latest)	8m 1s
build-lint-test (3.14, macos-arm)	7m 53s
build-lint-test (3.14, ubuntu-latest)	7m 16s
build-lint-test (3.10, windows-latest)	8m 39s
build-lint-test (3.10, ubuntu-latest)	6m 58s
build-lint-test (3.14, macos-intel)	9m 26s
build-lint-test (3.10, macos-intel)	12m 55s
	1h 9m 42s

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