model : support for LlamaBidirectionalModel architecture (#18220)

* model: llama-embed-nemotron

* minor: python lint

* changed arch-name

* templated llm_build_llama to be used for both llama and llama-embed arch

src/models/models.h

@@ -303,6 +303,7 @@ struct llm_build_llada_moe : public llm_graph_context {
     llm_build_llada_moe(const llama_model & model, const llm_graph_params & params);
 };
 
+template <bool embed>
 struct llm_build_llama : public llm_graph_context {
     llm_build_llama(const llama_model & model, const llm_graph_params & params);
 };