[Diffusion] Add cache-dit and unify diffusion cache backend interface (#250)

Signed-off-by: samithuang <285365963@qq.com>
Signed-off-by: SamitHuang <285365963@qq.com>
Signed-off-by: Samit <285365963@qq.com>
Co-authored-by: Jiangyun Zhu <riverclouds.zhu@qq.com>

tests/diffusion/cache/__init__.py

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+"""
+Unit tests for cache backends (cache-dit and teacache).
+"""