[Core] Add AttentionState abstraction (#7663)

tests/worker/test_model_input.py

@@ -5,6 +5,7 @@ import torch
 
 from vllm.attention import AttentionMetadata, AttentionMetadataBuilder
 from vllm.attention.backends.abstract import AttentionBackend
+from vllm.attention.backends.utils import CommonAttentionState
 from vllm.model_executor import SamplingMetadata
 from vllm.model_executor.pooling_metadata import PoolingMetadata
 from vllm.worker.embedding_model_runner import (
@@ -29,7 +30,11 @@ class MockAttentionBackend(AttentionBackend):
 
     @staticmethod
     def get_builder_cls() -> Type["AttentionMetadataBuilder"]:
-        raise AttentionMetadataBuilder
+        return AttentionMetadataBuilder
+
+    @staticmethod
+    def get_state_cls() -> Type["CommonAttentionState"]:
+        return CommonAttentionState
 
     @staticmethod
     def get_kv_cache_shape(