ContactAvatarBuilder works with SignalServiceAddress
Currently this only functions with the GRDB adapter. There are other asserts
triggered in yap extensions.
Tests from `receivedEnvelopeData`, which is called by e.g. the websocket or the
messageFetcherJob through the message processing pipeline until the UIDatabase
is notified with the new message and thread.
Includes some test helpers to initialize sessions and encrypt/decrypt messages.
