Major overhaul of JSON serialization/deserialization:
- Introduce AcJsonSerializerOptions for reference handling and max depth
- Centralize type checks, primitive/collection logic in JsonUtilities
- Add depth limiting to serializer/deserializer (MaxDepth support)
- Make $id/$ref reference handling optional via options
- Unify and simplify public API (ToJson, JsonTo, CloneTo, CopyTo, etc.)
- Improve primitive, enum, and collection handling and caching
- Refactor contract resolver and merge logic to use new utilities
- Remove redundant code, centralize string escaping/unescaping
- Update all tests and benchmarks to use new API and options
- Fix minor bugs and improve error handling and validation
This modernizes and unifies the JSON infrastructure for better performance, flexibility, and maintainability.