Add comprehensive JSON support via the Json module:
- Parse JSON strings with Json.parse() returning Result<Json, String>
- Stringify with Json.stringify() and Json.prettyPrint()
- Extract values with Json.get(), getIndex(), asString(), asInt(), etc.
- Build JSON with constructors: Json.null(), bool(), int(), string(), array(), object()
- Query with Json.isNull() and Json.keys()
Includes example at examples/json.lux demonstrating building, parsing,
and extracting JSON data with file I/O integration.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
