Parallelize box_blur_loop()

3 jobs for filter-perf-improvements in 9 minutes and 7 seconds (queued for 177 minutes and 46 seconds)
latest
Status Job ID Name Coverage
  Test
passed #78059
fedora test

00:08:45

 
  Lint
manual #78061
allowed to fail manual
clippy
passed #78060
rustfmt

00:00:22