Cache: init empty cache when use_cache (#34274)

* fix

* fix tests

* fix copies

* add docs

* Revert "add docs"

This reverts commit 32d35634f12ba02781d2ebdee0c8dcfbe992a7b9.

* qwen move deltas

* mllama can potentiall fullgraph compile

* enable mllama compile and fix tests

* remove mllama fixes

tests/generation/test_utils.py

@@ -1531,6 +1531,14 @@ class GenerationTesterMixin:
             embed_dim = getattr(text_config, "d_model", text_config.hidden_size)
             per_head_embed_dim = embed_dim // num_attention_heads
 
+            # some models have diffent num-head for query vs key/value so we need to assign correct value
+            # BUT only after `per_head_embed_dim` is set
+            num_attention_heads = (
+                text_config.num_key_value_heads
+                if getattr(text_config, "num_key_value_heads", None) is not None
+                else num_attention_heads
+            )
+
             past_kv = outputs["past_key_values"]
             self.assertEqual(len(past_kv), num_hidden_layers)