mtp: support for gemma-4 E2B and E4B assistants (#24282)

* models: update converter to support smaller assistants

* models: add masked_embd tensors to gemma4-assist arch

* gemma-4: remove temp debug for conversion

* gemma-4-mtp: filter out masked_embedding tensors during conversion

gguf-py/gguf/tensor_mapping.py

@@ -37,6 +37,14 @@ class TensorNameMap:
             "model.embed",                               # talkie
         ),
 
+        # Masked embeddings
+        MODEL_TENSOR.MASKED_EMBD_CENTROIDS: (
+            "masked_embedding.centroids",                # gemma-4 E2B/E4B assistants
+        ),
+        MODEL_TENSOR.MASKED_EMBD_ORDERING: (
+            "masked_embedding.token_ordering",           # gemma-4 E2B/E4B assistants
+        ),
+
         # Token type embeddings
         MODEL_TENSOR.TOKEN_TYPES: (
             "embeddings.token_type_embeddings",  # bert nomic-bert