listing: add flag to show file sizes

[marcospb19]

Add a flag like ouch list archive.tar.gz --show-size that shows the file size for each listed entry.

This requires that we read the contents of each entry instead of just their name, so it's more computationally heavy, adding this flag shouldn't make the default behavior slower.

Originally posted by @ofek in #1000

[marcospb19]

I think it's OK if this is not the default, as it pollutes the output and we'll be adding the ouch info command suggested in #1000, which should already tell the archive size.