_subdiagrams only returns diagrams of the last dim in homology_dimensions

[giotto-ai]

_subdiagrams only returns diagrams of the last dim in homology_dimensions

[ulupo]

It is also worth noting that this impacts performance, however slightly. Perhaps removing the loop and taking an integer instead of iterable as argument is the cleanest option. @gtauzin what do you think? I also agree that the method could be made public, but in that case I'm not sure how we would make it visible in the docs page.

[ulupo]

Fixed by #439.