Cleanup basic and entrypoint test organisation

[hmellor]

Supersedes #27747:

• Don't call basic test files individually
• Move the unit tests into a unit directory so we don't have to manually ignore everything else
• Move openai/tool_parsers into the unit tests because that's what they are

[gemini-code-assist]

Code Review

This pull request provides a good cleanup of the entrypoint tests. The main changes involve reorganizing test files into a new tests/entrypoints/unit directory, which improves the test structure by separating unit tests. The CI pipeline configuration in .buildkite/test-pipeline.yaml has been updated to reflect these changes, simplifying the test execution commands. Another notable improvement is in test_collective_rpc.py, where a manual GPU check is replaced with a pytest.mark.multi_gpu_test decorator, which is a cleaner approach. Overall, these changes enhance maintainability and clarity. I have not identified any issues of high or critical severity.

[chatgpt-codex-connector]

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[chaunceyjiang]

Thanks~

[hmellor]

Closing as this is now too stale