Progress indicator for `xcvm install`

[CraigSiemens]

The xip --expand takes a long time to run and doesn't report any kind of progress itself.

Possible Ideas:

• investigate if there's any way to estimate the progress, maybe based on the file size as it's being expanded
• add some kind of activity indicator to at least show something's happening
• show elapsed time

[CraigSiemens]

Since xcvm is now using unxip, it's main function shows how to track progress.

https://github.com/saagarjha/unxip/blob/main/unxip.swift#L1595-L1609