DiffService: initailize all methods with not_implemented

Also, link them with their respective issue on heptapod.
4 jobs for topic/default/diff-service in 1 minute and 3 seconds (queued for 1 second)
Status Job ID Name Coverage
  Main
passed #156209
tests-current

00:00:37

100.0%
 
  Compat
passed #156210
check-sdist

00:00:20

passed #156212
tests-hg-default

00:00:25

100.0%
passed #156211
tests-hg-stable

00:00:25

100.0%