Refactor size calculations in layers and backend

include/backend.hpp

@@ -28,6 +28,7 @@ class Backend {
     std::optional<DType> default_dtype;
   public:
 
+    // Dtypes
     virtual bool supports_dtype(DType dtype) const = 0;
     virtual void set_default_dtype(DType dtype) = 0;
     virtual DType get_default_dtype() const = 0;

include/module.hpp

@@ -15,10 +15,6 @@ class Module {
 
     CUDANet::Shape output_shape();
 
-    size_t input_size();
-
-    size_t output_size();
-
     void register_layer(const std::string& name, Layer* layer);
 
     void register_module(Module& module);

include/tensor.hpp

@@ -16,6 +16,19 @@ enum class DType
     // INT32,  // Not implemented yet
 };
 
+size_t dtype_size(DType dtype) {
+    switch (dtype)
+    {
+    case DType::FLOAT32:
+        return 4;
+        break;
+    
+    default:
+        throw std::runtime_error("Unknown DType");
+        break;
+    }
+}
+
 class Tensor
 {
 public: