[V0 deprecation] Removal V0 structured outputs

[aarnphm]

This PR is a continuation of removal for V0, starting with structured outputs

Signed-off-by: Aaron Pham contact@aarnphm.xyz

[github-actions]

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[gemini-code-assist]

Summary of Changes

Hello @aarnphm, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request is a continuation of the effort to remove V0 features, specifically targeting structured output capabilities. It deprecates and removes the guided decoding functionality from the V0 engine, ensuring that users are directed towards the V1 engine for these advanced output controls. This change simplifies the codebase by removing legacy components and clarifies the supported feature set for different engine versions.

Highlights

• Deprecation of V0 Structured Outputs: This pull request explicitly removes support for V0 structured outputs. Attempts to use guided_decoding parameters with the V0 engine will now raise a ValueError, directing users to switch to the V1 engine for this functionality.
• Removal of Guided Decoding Logic: The core logic responsible for building guided decoding logits processors, including the build_guided_decoding_logits_processor_async function and related imports, has been removed from both vllm/engine/async_llm_engine.py and vllm/engine/multiprocessing/client.py.
• Removal of Guided Decoding Tests: The test_mistral_guided_decoding function, which previously validated Mistral's guided decoding capabilities using JSON schema, has been removed from tests/models/language/generation/test_mistral.py, aligning with the deprecation of V0 structured outputs.

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[gemini-code-assist]

Code Review

This PR removes V0 structured outputs, replacing them with ValueErrors that guide users to V1. I've pointed out a minor typo in the new error messages.

[WoosukKwon]

@aarnphm Thanks for doing this! Could you please check the CI failures?

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @aarnphm.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[hmellor]

Superseded by #21347