feat: add llguidance grammar support to MaskedTag and update related functionality

[Ki-Seki]

Fixes #52

[codecov]

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✅ All modified and coverable lines are covered by tests.

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[Copilot]

Pull Request Overview

This PR adds support for custom CFG (Context-Free Grammar) definitions to MaskedTag, allowing users to specify structured generation constraints beyond regex patterns. The implementation ensures that only one constraint type (regex or grammar) can be used per tag and validates grammar syntax against LLGuidance specifications.

Key changes:

• Added grammar field to MaskedTag with mutual exclusivity with regex
• Implemented grammar validation in MaskedTag.__post_init__ to ensure proper syntax and prevent reserved rule name conflicts
• Updated build_cfg to handle tags with custom grammars by removing the start: prefix and embedding the rules

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/gimkit/schemas.py	Added grammar field to MaskedTag dataclass and implemented validation logic including empty string checks, reserved name conflicts, start rule requirement, and syntax validation
src/gimkit/dsls.py	Refactored grammar validation into standalone function, added constants for CFG rule naming and docs URL, updated build_cfg to handle tags with custom grammar by stripping start: prefix
tests/test_schemas.py	Added tests for grammar validation including empty string, reserved names, missing start rule, and invalid syntax; updated global variable assertions to include grammar field
tests/test_dsls.py	Updated test expectations to use new masked_tag_ prefix and added test case for building CFG with custom grammar
tests/models/test_utils.py	Updated assertion to expect new masked_tag_ rule naming convention

[Copilot]

Pull Request Overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.