Element-R: Wire up remaining bits of /sync response

[richvdh]

Currently, when we get a /sync response back from the server, we only feed the to-device messages into the rust OlmMachine. We also need to wire up:

• device lists
• one_time_key_counts
• unused_fallback_keys

[richvdh]

Reopening this: matrix-org/matrix-js-sdk#3215 doesn't handle the device lists.