[core] cudagraph output with tensor weak reference (#9724)

Signed-off-by: youkaichao <youkaichao@gmail.com>

csrc/torch_bindings.cpp

@@ -18,6 +18,9 @@
 TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
   // vLLM custom ops
 
+  ops.def("weak_ref_tensor(Tensor input) -> Tensor");
+  ops.impl("weak_ref_tensor", torch::kCUDA, &weak_ref_tensor);
+
   // Attention ops
   // Compute the attention between an input query and the cached
   // keys/values using PagedAttention.