feat(gdscript): add .gd extraction support (#697)

[TPAteeq]

Closes #697

Summary

• Add a dedicated tree-sitter GDScript extractor for .gd files.
• Wire GDScript into detection, dispatch, extractor registry, language-family guards, and analysis.
• Add the optional graphifyy[gdscript] dependency using a tree-sitter-compatible language-pack release.
• Document GDScript support and installation.

Extraction coverage

• Named and implicit script classes
• Functions, members, constants, signals, enums, and inner classes
• Identifier and res:// inheritance
• Typed member references
• Type.new() instantiations
• Same-script calls
• preload() and load() dependencies
• Cross-file type resolution

Godot built-ins are filtered to avoid noisy graph hubs, ambiguous receiver calls are not guessed, and unresolved type stubs use a reserved namespace to prevent
collisions with file nodes.

Validation

• uv run pytest -q — 3,119 passed, 30 skipped
• Ruff passed
• Pyright passed
• Package build passed
• graphify update . completed successfully