Implement possibility to handle already-generated packNGos

[gian-didom]

The packNGo function is buggy, slow, and is also different across multiple MATLAB versions.
The currently-implemented modifiedPackNGo is just a palliative, but it cannot guarantee the same functionality of the original packNGo across different MATLAB versions. As an instance, it does not work on MATLAB 2020a.

The timeline for fixing this feature is the following:

• Enable option -pack to specify the already-packed code
• Implement custom packNGo that is cross-platform and cross-version