Expand ProductFootprint object data model.

[JohnVonNeumann]

The ProductFootprint class does not implement a full python data model, making interactions with the instance a bit of an annoyance, naturally there are automatically defined dunder methods but a more explicit approach is preferable.

This tickets does not need to implement every dunder method in the object model, but the core/usual suspects would be preferable even if it's just to set the tone and standard for future developments.

A list of what would be desirable is:

• dict
• str
• repr