[V1] Allow sliding window + prefix caching

[WoosukKwon]

The KV cache manager in V1 ignores sliding window, so prefix caching is compatible with sliding window attention.

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[comaniac]

LGTM. Do we have a test for it?

[DarkLight1337]

tests/prefix_caching/test_disable_sliding_window.py::test_disable_sliding_window fails using V1 on main - perhaps we can update this test in this PR?