feat(architecture): extract code2toon package for TOON format parsing and diffing

[tom-sapletta-com]

Summary

• Extracted TOON (Topology Oriented Object Notation) specification, parser, validator, and diff engine into standalone package code2toon (v0.1.0) under packages/code2toon.
• code2toon provides:
  • Strongly-typed models: ToonDocument, ToonHeader, FunctionEntry.
  • Multi-format parser: parse_toon_content, load_toon, load_toon_document, is_toon_file.
  • Structural schema validator: ToonValidator, validate_toon.
  • Architectural drift diffing engine: diff_toon, ToonDiffResult (tracks complexity delta, additions/removals, and resolved/introduced code smells).
• Re-exported in code2llm/parsers/toon_parser.py with transparent fallback to embedded implementation if code2toon is not present.
• Added code2toon to pyproject.toml optional dependencies ([project.optional-dependencies] toon) and dev dependencies.
• Verified with 359/359 pytest tests passing.