Refactoring request for Study export function

[laurent-laporte-pro]

Description

This ticket is a technical request in order to refactor the Study export function export_study_flat located in the antarest.study.storage.utils package. The purpose of this function is to copy a Study to a destination directory with the simulation output (if this option is selected).

The current implementation needs improvement in terms of code organization and responsibility separation. I believe the following changes will enhance the overall design and maintainability of the codebase.

1. Move the export function to the antarest.study.storage.abstract_storage_service module:
   Currently, the export function resides in the utils package. To align with the code structure and improve coherence, I propose relocating the function to the antarest.study.storage.abstract_storage_service module.

2. Separate file copying and matrix denormalization responsibilities:
   The export function currently combines the tasks of file copying and matrix denormalization. It would be beneficial to separate these responsibilities.

3. Furthermore, I suggest implementing the denormalization directly within the two calling functions: VariantStudyService.export_study_flat and RawStudyService.export_study_flat. This approach will distribute the responsibility more effectively.

Tasks

• refactor the code (the function can be renamed if necessary),
• add the missing documentation,
• adjust and improve unit tests regarding export_study_flat,
• make sure VariantStudyService.export_study_flat and RawStudyService.export_study_flat are corectly tested.