llama : support LiquidAI LFM2-MoE hybrid model (#16464)

* llama : support LiquidAI LFM2-MoE hybrid model

Add support for [LiquidAI/LFM2-8B-A1B](https://huggingface.co/LiquidAI/LFM2-8B-A1B) model.
For more information about models, please read [the blog post](https://www.liquid.ai/company/news).

[HF PR](https://github.com/huggingface/transformers/pull/41401)
[GGUFs](https://huggingface.co/LiquidAI/LFM2-8B-A1B-GGUF)

* Do not use defaultdict

* Address PR feedback

src/llama-arch.h

@@ -97,6 +97,7 @@ enum llm_arch {
     LLM_ARCH_SMOLLM3,
     LLM_ARCH_OPENAI_MOE,
     LLM_ARCH_LFM2,
+    LLM_ARCH_LFM2MOE,
     LLM_ARCH_DREAM,
     LLM_ARCH_SMALLTHINKER,
     LLM_ARCH_LLADA,