Real-llama.cpp backend for erllama_model.

Owns a model_ref and a context_ref from erllama_nif. The gen_statem hands its decode/kv operations through this module; this module forwards to the NIF.

Config (passed through erllama_model:start_link/2): model_path :: file:name() | binary() (required) model_opts :: map() (forwarded to erllama_nif:load_model/2) context_opts :: map() (forwarded to erllama_nif:new_context/2)

model_opts and context_opts flow through to the NIF unchanged. See erllama_nif:load_model/2 and erllama_nif:new_context/2 for the full set of recognised keys, including the llama.cpp option passthroughs split_mode, main_gpu, tensor_split, flash_attn, type_k, and type_v.