ENH: Store more data as private members to speed up the processes

[remi-braun]

We should store all the data that are time-consuming (at least not immediate) and lightweight (floats or even vectors) in order to speed up the recomputation. These would be computed only if needed.

Hereunder is a premilinary list (for product):

• extent
• footprint
• mean_az, mean_el
• crs
• default_transform

And why not:

• condensed_name
• datetime
• date

Other product_classes could have others to add.

They could be accessed as regular members through a @property -> this will break things !

[remi-braun]

Need python 3.8 for @functools.cached_property and python 3.9 for @functools.cache 😰