[Fix] Use new add_kernel_to_copy() function

Context

This MR (MR0) broke the export by implementing a new way to handle the kernels_to_copy feature.
This is fixed in this MR (MR1) which changes aidge_core to implement a deprecation system for this specific change.

However, the current MR aims to update the way kernels_to_copy is used to adopt the new approach, solving the issue without having to wait for the MR1 to be merged.

Modified files

• operators.py : New kernels_to_copy method;