The sending half of the notifications channel(s) used to send
notifications about best BEEFY block from the gadget side.
The receiving half of a notifications channel used to receive
notifications about best BEEFY blocks determined on the gadget side.
The sending half of the notifications channel(s) used to send notifications
about versioned finality proof generated at the end of a BEEFY round.
The receiving half of a notifications channel used to receive notifications
about versioned finality proof generated at the end of a BEEFY round.