[Structured Output] Replace apply_grammar_bitmask() method with that in vllm to avoid maintenance

[shen-shanshan]

What this PR does / why we need it?

Replace apply_grammar_bitmask() method with that in vllm to avoid maintenance.

• vLLM version: v0.11.0rc3
• vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0

[gemini-code-assist]

Code Review

This pull request refactors the code to use the apply_grammar_bitmask function from the upstream vLLM library, removing the local implementation. This is a positive change that reduces code duplication and improves maintainability. The implementation correctly handles the necessary tensor manipulations, such as moving logits to the CPU and handling dtype conversions, which were previously part of the removed method. The changes appear correct and beneficial.

[github-actions]

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[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[shen-shanshan]

CC @wangxiyuan