Introduces Toon (Token-Oriented Object Notation), a new serialization format designed for LLM readability and token efficiency. Adds core Toon serializer, options, attribute system (ToonDescriptionAttribute), and comprehensive documentation. Supports explicit type metadata, smart fallback/placeholder logic, multi-turn workflows, reference handling, and multi-line strings. No breaking changes; Toon is opt-in and complements existing JSON/binary serializers.
