* feat/overseer: introduce closure init
Enables removal of the connected/disconnected overseer state.
* feat/overseer: allow replacement logic to access the original
Allows to re-use init-once types, which would otherwise error.
* feat/overseer: introduce external connector
Preparation for removal of `AllSubsystems`
which is another prerequisite for removing
the connect/disconnect state.
* fix/test: replace needs closure
* fixup
* simplify
* mea culpa
* all-subsystems-gen test
Bernhard Schuster