The `josh.meanings.protocols.cluster-model` namespace defines a protocol for
manipulating cluster models that have already been trained. 

The `PClusterModel` protocol defines the interface for cluster model 
implementations, including methods for saving and loading the model data, and 
classifying points using the model.

Any implementation of the `PClusterModel` protocol must provide concrete 
implementations of the protocol methods, and adhere to the input and output 
specs defined in the protocol.