[2/N] move responses/serving _make_response_output_items logic to parser

[qandrew]

Purpose

as titled. by moving logic of the reasoning / tool calling into parser, each model can implement its own interpretation of how to parse. we can then migrate GPT-OSS into parser. And models that support parallel tool calling / interleaved reasoning can use the parser structure.

stacking on top of #32712, this is an implementation of #32713

Test Plan

vllm serve MiniMaxAI/MiniMax-M2   --tensor-parallel-size 4   --tool-call-parser minimax_m2   --reasoning-parser minimax_m2    --enable-auto-tool-choice --trust-remote-code

 curl -X POST "http://localhost:8000/v1/responses" \
    -H "Content-Type: application/json" \
    -H "Authorization: Bearer dummy-api-key" \
    -d '{
      "model": "MiniMaxAI/MiniMax-M2",
      "input": "What is the weather in Paris in Celsius today?",
      "tools": [
        {
          "type": "function",
          "name": "get_weather",
          "description": "Get the current weather in a given location.",
          "parameters": {
            "type": "object",
            "properties": {
              "location": { "type": "string" },
              "unit": { "type": "string", "enum": ["celsius", "fahrenheit"] }
            },
            "required": ["location", "unit"]
          }
        }
      ]
    }' | jq

Test Result

---

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[gemini-code-assist]

Code Review

This pull request introduces a unified Parser interface to handle both reasoning and tool parsing, consolidating logic previously spread across ReasoningParser and ToolParser. New files vllm/parser/__init__.py, vllm/parser/abstract_parser.py, vllm/parser/minimax_m2_parser.py, and vllm/parser/parser_manager.py have been added to support this new architecture. The OpenAIServing and OpenAIServingResponses classes have been updated to utilize this unified parser. While the overall goal of unifying the parsing logic is a good step towards better organization, there is a critical thread-safety concern with the _WrappedParser implementation.

[qandrew]

cc @yeqcharlotte @houseroad
diff is a bit harder to review, just look at the last 3 commits for now

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[mergify]

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

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

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[chaunceyjiang]

Keep the original comments.

[qandrew]

thanks for the catch, done

[chaunceyjiang]

I remember there should be an assertion here to check that content is not None. Please keep it.

[chaunceyjiang]

I remember there should be an assertion here to check that content is not None. Please keep it.

[qandrew]

thanks. a lot of the code is copied from _parse_tool_calls_from_content, which is still used in the chat completions flow

I'll put in a follow up diff so chat completions can use parser also

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[chaunceyjiang]

Thanks~