Use datetime.timedelta in openai_agents samples #1228

Job	Run time
build-lint-test (3.10, windows-latest)	7m 5s
build-lint-test (3.10, macos-arm)	7m 41s
build-lint-test (3.10, ubuntu-latest)	5m 56s
build-lint-test (3.10, macos-intel)	9m 35s
build-lint-test (3.14, ubuntu-latest)	6m 2s
build-lint-test (3.14, windows-latest)	6m 46s
build-lint-test (3.14, macos-intel)	9m 56s
build-lint-test (3.14, macos-arm)	6m 14s
	59m 15s

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