Refactor ModelType Enum to Extensible Interface-Based

[koosty]

Hey, I’ve been messing around with this project and ran into a snag—I can’t easily add my own custom models. The LLM model structure’s a bit tricky for me to wrap my head around, so I’m not super comfy trying to add new models myself. It’d be awesome if there was a way for users to drop in their own models without waiting for official support.

Description

This PR refactors the ModelType enum to an interface to make it extensible allowing new model types to be added without modifying existing code.

Motivation

New model types can be added via new ModelType implementations and registered without changing existing code.

ModelSupport.ModelType modelType = new ModelSupport.ModelType() {
    @Override
    public Class<? extends AbstractModel> getModelClass() {
        return Qwen2Model.class;
    }
    @Override
    public Class<? extends Config> getConfigClass() {
        return Qwen2Config.class;
    }
    @Override
    public Class<? extends Tokenizer> getTokenizerClass() {
        return LlamaTokenizer.class;
    }
};

ModelSupport.register("QWEN3", modelType);
AbstractModel model = ModelSupport.loadEmbeddingModel(new File("Qwen_Qwen3-Embedding-0.6B"), DType.F32, DType.I8);

[tjake]

Cool idea, thank you!