avatar: update to latest bumble server

This commit includes:
* Update to bumble `PairingDelegate` move.
* Update to the new way IO capability are overidden in the bumble server.
* Fix invalid use of `TestAbortAll` instead of `TestAbortClass`
* Normalize UUID string format accross Avatar.
* Add missing `@rpc` decorator to Gatt servicer methods.
* Remove now unecessary usage of `__repr__` for enums.
* Use mobly asserts instead of `assert` for better error messages, keep
  `assert` where necessary for the linter to be happy.

Bug: 278738537
Bug: 279027405
Test: avatar run
Change-Id: I5a800cdd94c9f4d88683c7b81fcae663d8ff8938