Fix UNIQUE constraint on storage_service_id during backup and transfer

[loucass]

Fixes #14954

Enabling backups during device transfer could hit UNIQUE constraint on recipient.storage_service_id (2067) and loop. Group import generated a random key without retry, so collision crashed the flow. Retry with new key up to 5 times and skip on persistent collision.

[loucass]

Small update on this one. I dug into the actual crash log and the failure is an UPDATE on the self account row, so I centered the fix there:
1- free that id inside the transaction
2- update self id to this id
3- then move the other row to a checked fresh id
If that ever fails, the row keeps a NULL id and the next sync repairs it by itself.

Also in this push:

• Restoring a group that already exists just reuses it now.
• A failed group no longer poisons later steps with a fake id.
• Inserts retry both ways a duplicate can surface, max 5 tries, then fail
  loud with an internal report instead of looping forever.

Added tests for all three in RecipientTableTest — green here:
https://github.com/loucass/Signal-Android/actions/runs/33978175898

Happy to adjust anything to match how you'd like it done.