Resource field for storing custom objects with manual JSON serialization.

SerializableRField stores instances of SerializableObjectJson subclasses, which provide custom serialize() and deserialize() methods for converting between Python objects and JSON-compatible representations.

When a Resource is saved: - The object's serialize() method is called - The resulting JSON data is stored in KV_STORE

When a Resource is loaded: - The JSON data is retrieved - The object's deserialize() class method is called to reconstruct the object

This is useful for: - Custom objects with specific serialization requirements - Legacy objects that need special handling - Objects that can't use Pydantic (use ModelRField for Pydantic models) - Fine-grained control over serialization format

Storage behavior: - Stored in KV_STORE by default - Not included in dict views by default (can be changed) - Uses custom serialize/deserialize methods

Example: ```python class CustomData(SerializableObjectJson): def init(self, value: int = 0): self.value = value

    def serialize(self) -> Dict:
        return {'value': self.value}

    @classmethod
    def deserialize(cls, data: Dict) -> 'CustomData':
        return cls(value=data['value'])

class MyResource(Resource):
    # Default value is object_type() (new instance)
    data = SerializableRField(object_type=CustomData)

    # Included in dict view
    visible_data = SerializableRField(
        object_type=CustomData,
        include_in_dict_view=True
    )

# Usage
resource = MyResource()
resource.data = CustomData(value=42)
```

Note: - The object_type must be a subclass of SerializableObjectJson - Default value is a new instance of object_type (calls object_type()) - The object_type must have a no-argument constructor