[Build] Update Xgrammar to 0.1.25

[chaunceyjiang]

Purpose

v0.1.25 brings the structural tag. It also fixes a couple of problems regarding JSON schema and py.typed. It enhances the speed of grammar compilation and mask generation.

The new version of structural tags lays the foundation for refactoring the tool parser.
https://xgrammar.mlc.ai/docs/tutorials/structural_tag.html#example-1-tool-calling

Test Plan

Test Result

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
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• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
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[gemini-code-assist]

Code Review

This pull request updates the xgrammar dependency to version 0.1.25 and adapts the codebase to the new API. The changes in vllm/v1/structured_output/backend_xgrammar.py correctly use xgr.StructuralTag.from_legacy_structural_tag to create a StructuralTag object, which is now required by the updated library functions. The changes are straightforward, necessary for the version bump, and appear correct. I have no further comments.