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

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

src/llama-hparams.h

@@ -66,6 +66,7 @@ struct llama_hparams {
     float    expert_weights_scale = 0.0;
     bool     expert_weights_norm  = false;
     uint32_t expert_gating_func   = LLAMA_EXPERT_GATING_FUNC_TYPE_NONE;
+    uint32_t moe_every_n_layers   = 0;
 
     float f_norm_eps;
     float f_norm_rms_eps;