Add structured import and reference extraction

[andrew]

Adds structured Imports and Refs APIs for extracting consumed modules, local aliases, and filtered member references.

Covers Python, JavaScript and TypeScript, Go, Ruby, Rust, PHP, and Elixir, including multiline Python imports and CommonJS forms used by Hyrum.

Closes #27.

[Copilot]

Pull request overview

This PR introduces new public APIs to extract structured imports and filtered member references from source files across multiple languages, building on the existing Tree-sitter parsing infrastructure in outline.

Changes:

• Adds exported data models (ImportKind, Import, Ref) plus new Imports and Refs extraction APIs.
• Implements per-language import extraction (Python/JS/TS plus Hyrum-targeted ecosystems like Go/Ruby/Rust/PHP/Elixir) and receiver-filtered reference extraction.
• Refactors parsing into a shared parseSource helper and adds tests/benchmarks + README documentation.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
syntax.go	Adds exported ImportKind, Name, Import, and Ref types forming the new public API surface.
node.go	Introduces shared Tree-sitter node helpers used by both import and reference extraction.
import.go	Implements Imports and core Python/JS/TS import extraction.
import_hyrum.go	Adds additional import extraction implementations (Go/Ruby/Rust/PHP/Elixir) aligned with Hyrum use cases.
import_test.go	Adds unit tests covering multiple languages and edge cases (e.g., multiline Python imports, CommonJS).
ref.go	Implements Refs and shared member-access traversal for multiple languages.
ref_hyrum.go	Adds Ruby/PHP-specific reference extraction helpers.
ref_test.go	Adds unit tests validating receiver-filtered member extraction across languages.
syntax_bench_test.go	Adds benchmarks for Imports (Python/JS) and Refs (JS).
outline.go	Refactors parsing into reusable parseSource helper used by Outline/Imports/Refs.
README.md	Documents the new APIs and provides an example snippet.

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