`ucm`: show how many entities remain to be downloaded

[joshklop]

Hi! First-time user here. Unison looks exciting! Thanks for building it.

Is your feature request related to a problem? Please describe.

I am going through the quick start. After running project.create for the first time, the base Unison library is downloaded. I have a slow connection, so this takes a while and I don't know how long it will take until it finishes.

Describe the solution you'd like

Instead of the cli saying Downloaded 3 entities, maybe it could say something like Downloaded 3 out of 13797 entities to give rough estimation of how long it will take.

Describe alternatives you've considered

#5094 and #4875 appear to be related.

Additional context

n/a