Add qvm-set-wallpaper

[hippalectryon-0]

Closes QubesOS/qubes-issues#215

This adds qvm-set-wallpaper, which safely converts an image from another VM using qubes.GetImageRGBA and sets it as the current VM's wallpaper.

Note: parts of this PR, e.g. utests, are GenAI generated and human-reviewed

TODO before marking as ready:

• test on actual VM, if possible with different DE

[codecov]

Codecov Report

❌ Patch coverage is 96.47059% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.38%. Comparing base (277a03a) to head (e27dc3f).

Files with missing lines	Patch %	Lines
qubesadmin/tools/qvm_set_wallpaper.py	96.47%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #453      +/-   ##
==========================================
+ Coverage   76.20%   76.38%   +0.18%     
==========================================
  Files          53       54       +1     
  Lines        9359     9444      +85     
==========================================
+ Hits         7132     7214      +82     
- Misses       2227     2230       +3     

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[ben-grande]

Assuming I understood this correctly, it is doing the conversion in the same qube the image is in. This has the problem of trusting the image. Because you downloaded the image to that qube, doesn't mean you trust to open it in that qube. That is why conversions happen in disposable qubes.

In short:

• https://github.com/QubesOS/qubes-app-linux-img-converter/blob/main/rpm_spec/qimg-converter-dom0.spec.in
• https://github.com/QubesOS/qubes-app-linux-img-converter/blob/main/qvm-get-image

[marmarek]

TBH, I'm not sure if this is really a valid concern. If somebody doesn't trust the image, they can always call qvm-convert-img before doing anything else with the file. Which would be a good idea in that case anyway, to avoid for example file manager loading it for preview.

[ben-grande]

I think this PR should be in https://github.com/QubesOS/qubes-app-linux-img-converter