[1/N][Attention] Restructure attention: move files (#31916)

Signed-off-by: Matthew Bonanni <mbonanni@redhat.com>

tests/v1/attention/utils.py

@@ -7,8 +7,6 @@ from dataclasses import dataclass
 import pytest
 import torch
 
-from vllm.attention.backends.abstract import AttentionImpl
-from vllm.attention.backends.registry import AttentionBackendEnum
 from vllm.config import (
     CacheConfig,
     CompilationConfig,
@@ -20,6 +18,8 @@ from vllm.config import (
     VllmConfig,
 )
 from vllm.config.model import ModelDType
+from vllm.v1.attention.backend import AttentionImpl
+from vllm.v1.attention.backends.registry import AttentionBackendEnum
 from vllm.v1.attention.backends.utils import (
     AttentionMetadataBuilder,
     CommonAttentionMetadata,