Open the initial response using the associated data and this
UnidirectionalSenderChannel.
This method will decrypt the given message coming from the other side of this channel and fully establish the HPKE channel, enabling bidirectional communication.
The unidirectional HPKE sender channel.
This channel is created when we seal the initial plaintext and we wait for the initial response. from the other side.
See HpkeSenderChannel.establishChannel.