[Performance]: very slow performance for nested list with length constraints

[naturomics]

Proposal to improve performance

No response

Report of performance regression

No response

Misc discussion on performance

See this report at xgrammar issue.

• env:

  • vllm: 0.9.1
  • xgrammar: 0.1.19

• Structured json schema:

class Table(BaseModel):
   content: conlist(conlist(str, min_length=5, max_length=10), min_length=5, max_length=10)

json_schema = Table.model_json_schema()

This schema leads to very low thoughput (< 3 tokens/s).
Is there any way to improve performance?

Your current environment (if you think it is necessary)

The output of `python collect_env.py`

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