Rename perf -> pyperf

It got a rename and a new home: https://github.com/psf/pyperf
I executed:

  rg '\-m perf' -l | xargs sed -i 's/\-m\ perf/\-m\ pyperf/g'
2 jobs for topic/default/mpi4py-fft-pyperf in 5 minutes and 30 seconds
Status Job ID Name Coverage
  Test
passed tests #119137

00:04:14

passed tests_pythran_mpi #119138

00:05:30