feat [#454]: implement multi-architecture image handling

[NN708]

This PR resolves the Manifest does not contain layer property error by implementing proper handling of manifest lists of multi-architecture container images. ABRoot now automatically selects and fetches the correct image manifest for the host system's architecture while maintaining full backward compatibility.

Before:

$ pkexec abroot -V upgrade -c
...
 INFO  Checking for system updates...
(Verbose) ABSystem.CheckUpdate:info:running...
(Verbose) Registry.HasUpdate:info:Checking for updates ...
(Verbose) Registry.GetToken:info:call URI ishttps://ghcr.io/token?scope=repository:vanilla-arm/desktop:pull&service=ghcr.io
(Verbose) Registry.GetManifest:info:running...
(Verbose) Registry.GetManifest:info:call URI ishttps://ghcr.io/v2/vanilla-arm/desktop/manifests/test
(Verbose) Registry.GetManifest:err(4.000000):<nil>
(Verbose) Registry.HasUpdate:err(1.000000):Manifest does not contain layer property
  ERROR   Manifest does not contain layer property

After:

$ pkexec abroot -V upgrade -c
...
 INFO  Checking for system updates...
(Verbose) ABSystem.CheckUpdate:info:running...
(Verbose) Registry.HasUpdate:info:Checking for updates ...
(Verbose) Registry.GetToken:info:call URI is https://ghcr.io/token?scope=repository:vanilla-arm/desktop:pull&service=ghcr.io
(Verbose) Registry.GetManifest:info:running...
(Verbose) Registry.GetManifestJSON:info:call URI is https://ghcr.io/v2/vanilla-arm/desktop/manifests/test
(Verbose) Registry.GetManifest:info:detected multi-architecture manifest list
(Verbose) Registry.GetManifest:info:selected manifest for architecture amd64, digest: sha256:5a8c9cb55570ea328dfe9bef66e6fab1a97a3e726ff4826b3f833075dda96a8b
(Verbose) Registry.GetManifestJSON:info:call URI is https://ghcr.io/v2/vanilla-arm/desktop/manifests/sha256:5a8c9cb55570ea328dfe9bef66e6fab1a97a3e726ff4826b3f833075dda96a8b
(Verbose) Registry.GetManifest:info:success
(Verbose) Registry.HasUpdate:info:update available. Old digest: sha256:42407ab9f5f3e1423e827da3ce6efe036b226c511e8031c0686e343bdaa9b609, new digest: sha256:5a8c9cb55570ea328dfe9bef66e6fab1a97a3e726ff4826b3f833075dda96a8b
 INFO  There is an update for your system.
...

Resolves #454.