[Client] Restructure code

[Zapharaos]

https://github.com/golang-standards/project-layout/tree/master

• [x] create internal package for downloader
• [x] move huggingface into pkg
• [x] refactor utils : move into subpackages
• [x] cmd/ contains and uses explicit code from internal/

[Zapharaos]

Waiting for issues #46 and #55 to be completed. Then we will see if this issue needs to be updated

[Zapharaos]

More in depth restructuring will be done through other issues.

Examples :

• more mockers, more unit tests => better coverage
• moving the remaining model code from cmd to controller