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/llama-arch.h

@@ -119,6 +119,7 @@ enum llm_arch {
     LLM_ARCH_RND1,
     LLM_ARCH_PANGU_EMBED,
     LLM_ARCH_MISTRAL3,
+    LLM_ARCH_LLAMA_EMBED,
     LLM_ARCH_UNKNOWN,
 };