Show status when downloading assets

[wch]

This change makes it so that the asset download status is printed, and updated every 1 second. This is helpful when on a not-super-fast internet connection so that the user has an idea what is happening and how long they will have to wait.

❯ shinylive assets download
Downloading https://github.com/posit-dev/shinylive/releases/download/v0.7.0/shinylive-0.7.0.tar.gz...
5%, 6604 KB/s, 20.4/343.6 MB

It adds an option --no-status to disable the displaying of the status. However, as of right now, that option is only available when running shinylive assets download. It's not there if you run shinylive export ... and the assets are automatically downloaded. I think that's OK, since I believe it would be an unusual case where someone wants to run shinylive export and suppress the status, and for those use cases, they could just run shinylive assets download --no-status first.

[gadenbuie]

LGTM! I agree with your choice a about the --no-status flag, although I would have called it --quiet (that would be the flag I'd try before reading the docs).

[wch]

I actually initially went with --quiet, but then I realized it wasn't actually quiet because it was still displaying the URL that's being downloaded.

I could be persuaded either way with whether the option should be --quiet or --no-status, but if it were --quiet, then I think it should suppress the URL as well.