Avoid circular dep

Author: NicolasHug

src/torchcodec/_core/Cache.h

@@ -9,7 +9,6 @@
 #include <torch/types.h>
 #include <memory>
 #include <mutex>
-#include "src/torchcodec/_core/CUDACommon.h"
 
 namespace facebook::torchcodec {
 
@@ -96,6 +95,11 @@ class PerGpuCache {
   std::vector<std::unique_ptr<Cache<T, D>>> cache_;
 };
 
+// Forward declaration of getDeviceIndex which exists in CUDACommon.h
+// This avoids circular dependency between Cache.h and CUDACommon.cpp which also
+// needs to include Cache.h
+int getDeviceIndex(const torch::Device& device);
+
 template <typename T, typename D>
 bool PerGpuCache<T, D>::addIfCacheHasCapacity(
     const torch::Device& device,