Allow blank constructors for pointer types.

src/Memory/BorrowedPtr.hpp

@@ -6,6 +6,7 @@ namespace Arbutils::Memory {
         T* _ptr;
 
     public:
+        inline BorrowedPtr() {};
         inline explicit constexpr BorrowedPtr(T* ptr) noexcept : _ptr(ptr){};
 
         inline constexpr T* GetUnsafe() noexcept { return _ptr; }