Refactor weaver-syntax tests and helpers

[leynos]

Summary

• Refactors the test harness and support utilities for the weaver-syntax crate, reorganising unit, behavioural, and end-to-end tests under crates/weaver-syntax. Adds extensive end-to-end and BDD test coverage with insta snapshots.
• Wires the weaver-syntax crate into the workspace and updates workspace test tooling and dependencies.
• Keeps and expands Tree-sitter-based syntactic analysis, language detection, pattern matching, and rewriting capabilities exposed by the weaver-syntax crate.
• Updates documentation surface (roadmap, users guide, and weaver design) to reflect the integrated weaver-syntax testing surface and components.

Changes

Crate and testing harness

• Added crates/weaver-syntax with modules for error handling, language detection, parsing, pattern compilation, matching, metavariables, rewriting, and syntactic locking.
• Refactored and reorganised tests under crates/weaver-syntax:
  • Unit, behavioural, and test harness modules (mod.rs, unit.rs, behaviour.rs) alongside a dedicated tests/ directory for end-to-end testing.
  • Behavioural tests and step definitions implemented in crates/weaver-syntax/src/tests/behaviour.rs with BDD scaffolding.
  • End-to-end tests added under crates/weaver-syntax/tests/e2e with associated insta snapshots and a feature file at crates/weaver-syntax/tests/features/weaver_syntax.feature.
• Introduced centralised metavariable handling and matcher infrastructure (metavariables.rs, matcher/ modules) to support pattern matching and rewriting in tests.
• Wired the weaver-syntax crate into the workspace with its own Cargo.toml and integration with workspace test tooling and dependencies.
• Updated workspace cargo dependencies to support the new crate’s test and development workflow.

End-to-end tests and snapshots

• Added comprehensive end-to-end tests and corresponding insta snapshot harnesses to validate language detection, parsing, pattern matching, and rewriting across languages.
• Included snapshots for language detection, parse errors, and validation failures.

Pattern matching, metavariables, and rewriting

• Introduced a complete pattern language with metavariable handling and capture representations.
• Implemented a rewriting engine with template substitution and change tracking.
• Added dedicated metavariables utilities and placeholder handling to support pattern compilation and matching in tests.

Syntactic locking and error reporting

• Implemented a Tree-sitter based syntactic lock to validate code prior to semantic checks.
• Added error reporting structures and parsers per-language, surfaced in tests and end-to-end snapshots.

Language detection and parsing support

• Implemented language detection from file extensions and path-based detection.
• Wired Tree-sitter-based parsers for Rust, Python, and TypeScript.

Documentation and roadmap

• Updated docs/roadmap.md to reflect the weaver-syntax crate integration and its testing surface.
• Updated docs/users-guide.md to describe the syntactic lock, pattern matching, and rewriting capabilities exposed by weaver-syntax.
• Expanded docs/weaver-design.md with an illustrative diagram of the weaver-syntax module and its components.

Workspace wiring

• Wired the weaver-syntax crate into the workspace, including its dedicated Cargo.toml and integration with workspace test tooling and dependencies.
• Adjusted workspace dependencies to support the new crate’s test and development workflow.

📎 Task: https://www.terragonlabs.com/task/2042b5de-5e37-46c2-95d5-9e20ce878851