[chore] various federatingdb tweaks (#4178)

after seeing a potential reported federating worker lockup i decided to start digging into the federatingdb code. this PR encompasses:
- removes one of our last unused interface types `federatingdb.DB{}`, replacing it with a struct type `*federatingdb.DB{}`
- in `transport.dereferenceLocal()` differentiates between an unsupported lookup type and ErrNoEntries to reduce unnecessary calls, and reduce potential lockups that may occur while trying to call our own endpoints that then call `federatingdb.Lock()`
- removes a bunch of the locks on follow state changes since the DB already synchronizes that
- removes the unnecessary `pub.Clock{}` struct field and type passed to the transport controller

frankly it would be great if we could remove the locking in `federatingdb.Lock()` and instead handle it ourselves as it gets very confusing trying to figure out what functions will have locks held. but i guess that's one for when we move further away from the go-fed/activity/pub package usage.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4178
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

cmd/gotosocial/action/server/server.go

@@ -271,7 +271,7 @@ var Start action.GTSAction = func(ctx context.Context) error {
 	intFilter := interaction.NewFilter(state)
 	spamFilter := spam.NewFilter(state)
 	federatingDB := federatingdb.New(state, typeConverter, visFilter, intFilter, spamFilter)
-	transportController := transport.NewController(state, federatingDB, &federation.Clock{}, client)
+	transportController := transport.NewController(state, federatingDB, client)
 	federator := federation.NewFederator(
 		state,
 		federatingDB,