[BUG]: Immediate sequence copies the input

It's not clear whether the `immediate_sequence` holds a view over an array or whether it copies the data to internal representation. Currently, it just copies everything ([example](https://godbolt.org/z/j6Kas3zs8)).

This is not ideal, because it's really easy to forget to make a view over for example a `std::vector` before passing it to the immediate sequence constructor.