fix: skip to initialize grammar backend when tokenizer is not supported

[jimoosciuc]

Motivation

FIXES: #464

Modifications

• skip to initialize grammar backend when tokenizer is not supported.
• add to_finish to support abort req in the middle; the current implementation causes the request to hang and never return.

Accuracy Tests

Benchmarking and Profiling

Checklist

• Please use English, otherwise it will be closed.
• The purpose of the PR, or link existing issues this PR will resolve.
• The test plan, such as providing test command.
• (Optional) The necessary documentation update.

[gemini-code-assist]

Summary of Changes

Hello @jimoosciuc, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the robustness of the system by addressing two critical areas: the handling of grammar backend initialization with various tokenizer types and the reliability of request abortion. It ensures that grammar-based generation only proceeds with supported tokenizers and provides a more controlled way to terminate requests, preventing potential hangs and improving overall system stability.

Highlights

• Grammar Backend Initialization: The system now gracefully handles unsupported tokenizer types for grammar-based generation. If a tokenizer is not compatible, the grammar backend initialization is skipped, and requests attempting to use grammar features will be aborted with a clear error message, preventing crashes or unexpected behavior.
• Improved Request Abort Mechanism: A new to_finish mechanism has been introduced to properly abort requests mid-process. This resolves an issue where requests could hang indefinitely when an abort signal was received, ensuring that all requests are terminated cleanly and resources are released.

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