fix default creation of empty unique ptr

[Fabi12345678910]

Hey there,
i have spend quite some time trying to get SimSYCL running on a local machine.
Unfortunately all tests regarding group operation failed.
I was able to nail this down to the creation default per operation data.

The creation is used e.g. in schedule.cc:272 and schedule.cc:274.
The behaviour of the current default creation is to create an empty unique pointer.
When this pointer is dereferenced inside the group operation implementation (group_operation_impl.hh:256, group_operation_impl.hh:258), the behavior is undefined according to https://en.cppreference.com/w/cpp/memory/unique_ptr/operator%252A.html

using std::make_unique will return a nonempty pointer
this also fixed all local test errors.

Machine details:
OS: Arch Linux Kernel Version 6.18.1-arch1-2
gcc, g++ version: 15.2.1 20251112