[Core] Enable regex support with xgrammar

[russellb]

xgrammar 0.1.12 has fixes that should allow us to turn on regex
support.

This PR is a draft pending 0.1.12 to make it to pypi mirrors
and for #12632 to merge first, since this would conflict with
the changes there.

[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.

🚀

[terrytangyuan]

Would it be a good idea to check xgrammar version and print out warning if they are using an old version?

[russellb]

Would it be a good idea to check xgrammar version and print out warning if they are using an old version?

hm, I'm not sure we do that other places. We just assume the code has what we express is required in the requirements files. You're on your own if you veer outside of that!

[mergify]

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

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

[Ubospica]

I think it should work fine with xgrammar. Thanks @russellb !

[russellb]

marked as a draft again as the pin to 0.1.11 is intentional to avoid a bug introduced in 0.1.13. I'll revisit this again after a release that resolves the bug in question.

#13338