feat: unify state holder api

build.gradle.kts

...de/justjanne/libquassel/client/session/BaseInitHandler.kt

...n/de/justjanne/libquassel/client/session/ClientSession.kt

...n/de/justjanne/libquassel/protocol/io/CoroutineChannel.kt

...stjanne/libquassel/protocol/syncables/HeartBeatHandler.kt

...stjanne/libquassel/protocol/syncables/ObjectRepository.kt

...e/libquassel/protocol/syncables/StatefulSyncableObject.kt

...tlin/de/justjanne/libquassel/protocol/util/StateHolder.kt

...stjanne/libquassel/protocol/util/StateHolderExtensions.kt