Fixed potential snapshot issue and added recovery for devices missing…

[HiccupHan]

… MLS state machine on start up

• For the issue where snapshot data may be encrypted with a newer encryption key:

  • Snapshot data now handled in two passes: first pass processes MLS commits, second pass processes data
  • Added retry queue in case another snapshot contains commits for new data

• For devices missing MLS state machines on startup:

  • Startup now checks the actual MLS group instead of treating cached keys as a working state machine
  • Generates a new deviceID
  • Rejoins the existing MLS group
  • Ordinary members have their abandoned MLS leaf removed by the master
  • Recovered owners remain secondary until explicitly made master; takeover then removes the abandoned owner leaf