feat: Gemma4 text generation support (CORE-30) (#13376)

* initial gemma4 support

* parity with reference implementation

outputs can 100% match transformers with same sdpa flags, checkpoint this and then optimize

* Cleanup, video fixes

* cleanup, enable fused rms norm by default

* update comment

* Cleanup

* Update sd.py

* Various fixes

* Add fp8 scaled embedding support

* small fixes

* Translate think tokens

* Fix image encoder attention mask type

So it works with basic attention

* Handle thinking tokens different only for Gemma4

* Code cleanup

* Update nodes_textgen.py

* Use embed scale class instead of buffer

Slight difference to HF, but technically more accurate and simpler code

* Default to fused rms_norm

* Update gemma4.py

comfy/utils.py

@@ -1446,10 +1446,3 @@ def deepcopy_list_dict(obj, memo=None):
     memo[obj_id] = res
     return res
 
-def normalize_image_embeddings(embeds, embeds_info, scale_factor):
-    """Normalize image embeddings to match text embedding scale"""
-    for info in embeds_info:
-        if info.get("type") == "image":
-            start_idx = info["index"]
-            end_idx = start_idx + info["size"]
-            embeds[:, start_idx:end_idx, :] /= scale_factor