albumartcache: Optimize frame rendering

Use the ability to set_device_scale on a cairo.Surface to remove two
steps in the frame drawing method.

Closes: #81
3 jobs for wip/mschraal/artrework in 21 minutes and 38 seconds (queued for 21 minutes and 18 seconds)
Status Job ID Name Coverage
  Check
passed #6814
pep8

00:05:35

passed #6813
pyflakes

00:04:34

 
  Build
passed #6815
build

00:11:28