model : Nomic Embed Text V2 with Mixture-of-Experts (MoE) architecture (#12466)

* Nomic Embed Text V2 with Mixture-of-Experts (MoE) architecture

- Adds MoE-based embedding model supporting multilingual embeddings.
- Selects architecture variant based on hyperparameter detection (MoE layers).
- Removes unnecessary subclass initialization checks for clarity.

https://www.nomic.ai/blog/posts/nomic-embed-text-v2

Co-authored-by: Jared Van Bortel <jared@nomic.ai>

* fix tokenizer

* don't rename this tensor

---------

Co-authored-by: Jared Van Bortel <jared@nomic.ai>

src/llama-arch.h

@@ -23,6 +23,7 @@ enum llm_arch {
     LLM_ARCH_REFACT,
     LLM_ARCH_BERT,
     LLM_ARCH_NOMIC_BERT,
+    LLM_ARCH_NOMIC_BERT_MOE,
     LLM_ARCH_JINA_BERT_V2,
     LLM_ARCH_BLOOM,
     LLM_ARCH_STABLELM,
@@ -110,6 +111,7 @@ enum llm_kv {
     LLM_KV_EXPERT_WEIGHTS_SCALE,
     LLM_KV_EXPERT_WEIGHTS_NORM,
     LLM_KV_EXPERT_GATING_FUNC,
+    LLM_KV_MOE_EVERY_N_LAYERS,
     LLM_KV_POOLING_TYPE,
     LLM_KV_LOGIT_SCALE,
     LLM_KV_DECODER_START_TOKEN_ID,