Show information while downloading debug symbols

### Is there an existing proposal for this?

- [x] I have searched the existing proposals

### Is your feature request related to a problem?

I tried pystack the first time, in a somewhat mediocre WiFi (capped to 20 MBit/s; I assume there are parts of the world where way less than that is common for many people). I used it on a [project](https://qutebrowser.org/) which has a lot of C++ debug symbols (via [QtWebEngine](https://wiki.qt.io/QtWebEngine)/Chromium).

Given the claims about performance in the readme, I was quite surprised when pystack only printed basic information (up to "The process died due receiving signal SIGSEGV"), and then hung for 3.5 minutes before printing a stack.

Only while investigating the issue, I figured out the culprit was downloading of a couple 100MB of debug information (if it's any indication, my `~/.cache/debuginfod_client/` is currently 1.7 GB), and printing of the stack was indeed lightning fast! 🚀

As an additional consideration, I'm often on metered networks (tethering via a mobile connection while abroad). With that, such a message would have made me realize what was going on so I could cancel the download before it burns all through my data.

### Describe the solution you'd like

At minimum, a "Downloading debug information..." would have helped here already. Ideally, some live updating progress like "Downloading debug information for libXYZ.so (1MB/100MB)" or somesuch would be even better.

### Alternatives you considered

Running pystack on pystack to realize why it was hanging :wink: