[V1] Structured Outputs + Thinking compatibility

[aarnphm]

This PR brings thinking support to structured outputs in V1. Currently, if you want to use thinking parser in conjunction with structured outputs, you have to use the V0 engine.

This is also compatible with speculative decoding

This PR also refactor the tokenizer onto the structured_output_manager in order to construct the reasoner.

I have also added tests to cover this case.

Tests with the following:

# thinking + structured outputs
vllm serve deepseek-ai/DeepSeek-R1-Distill-Qwen-32B --tensor-parallel-size 2 --max-model-len 32768 --guided-decoding-backend xgrammar --reasoning-parser deepseek_r1

# thinking + ngram + structured outputs
vllm serve deepseek-ai/DeepSeek-R1-Distill-Qwen-32B --tensor-parallel-size 2 --max-model-len 32768 --guided-decoding-backend xgrammar --reasoning-parser deepseek_r1 --speculative-config '{"method": "ngram", "num_speculative_tokens": 5, "prompt_lookup_max": 5, "prompt_lookup_min": 1}

Closes #14727

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.

💬 Join our developer Slack at https://slack.vllm.ai to discuss your PR in #pr-reviews, coordinate on features in #feat- channels, or join special interest groups in #sig- channels.

Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can either: Add ready label to the PR or enable auto-merge.

🚀

[aarnphm]

cc @gaocegege might be interested

[gaocegege]

Thanks for the PR. Please also update the docs https://docs.vllm.ai/en/latest/features/reasoning_outputs.html#structured-output

- VLLM_USE_V1=0 vllm serve deepseek-ai/DeepSeek-R1-Distill-Qwen-1.5B \
    --enable-reasoning --reasoning-parser deepseek_r1
+ vllm serve deepseek-ai/DeepSeek-R1-Distill-Qwen-1.5B \
    --enable-reasoning --reasoning-parser deepseek_r1

[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

[aarnphm]

seems like the failure on entrypoint is not related 😿