* Cosmetics, update logger `topics`
* Clean up sync/start methods in nimbus
why:
* The `protocols` list selects served (as opposed to sync) protocols only.
* The `SyncMode.Default` object is allocated with the other possible sync
mode objects.
* Add snap service stub to `nimbus`
* Provide full set of snap response handler stubs
* Bicarb for the latest CI hiccup
why:
Might be a change in the CI engine for MacOS.
6fb48517ba