prepareRecipientsForNewOutgoingMessage
open suspend override fun prepareRecipientsForNewOutgoingMessage(recipients: List<<Error class: unknown class>>): Either<CoreFailure, UsersWithoutSessions>
Verifies if this client can send messages to all the client recipients. Will fetch PreKeys and establish cryptographic sessions if needed.
Return
an error or holder UsersWithoutSessions with an optional list of users whose sessions are missing. Useful for sending a message to a partial list of users.