Categorize tests/kernels/ based on kernel type (#16799)

Signed-off-by: mgoin <mgoin64@gmail.com>

tests/kernels/attention/conftest.py

@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: Apache-2.0
+
+import pytest
+
+from vllm.utils import (create_kv_caches_with_random,
+                        create_kv_caches_with_random_flash)
+
+
+@pytest.fixture()
+def kv_cache_factory():
+    return create_kv_caches_with_random
+
+
+@pytest.fixture()
+def kv_cache_factory_flashinfer():
+    return create_kv_caches_with_random_flash