[Feat](Exports) Minor features for export generation

Context

Needed some features to generate the exports (needed for the cpp export refactor) :

• Now possible to generate a label tensor into the generate_main_cpp() function for result verification at runtime.
• Add a copy_folder() function and add a symlink argument to create symbolic links instead of simple file copy (help with dev process).
• Add a function to remove the optional inputs from the order_inputs list so that they are not exported.
• The ExportNode class now holds a static_folders variable acting as the existing static_files variable but for whole folders.
• Change the kernels_to_copy export node system as the old system had some limitations. Indeed, it was not possible to chose a destination path different from the source path. Also the copied kernel would be automatically included in the fwd file, sometime leading to unused includes. The new system is based on a list of dict holding, for each kernel file, the source and destination paths as well as a boolean to indicate if the kernel needs to be included in the forward file.

Modified files

• code_generation.py - Add copy_folder() function and symlink option.

• export_registry.py - Add static_folder : list of folders to export.

• scheduler_export.py - Calls the copy_folder() function to export the static_folders. Also change test_mode to dev_mode for more clarity. If the dev_mode is enabled, the copied files will be symbolic links to help with development.

• generate_main.py - Add label export.

• main.jinja - Add label export and change default folder for inputs/labels to ROOT/data.

• main_compare.jinja - Change default folder for inputs/labels to ROOT/data.

• export_utils.py - Add remove_optional_inputs() to remove the optional inputs of the graph before export.