Other(refactor): Sort safe.Mutex types before locking to prevent deadlocks

This change implements safe.Mutex and safe.RWMutex, which wrap the
sync.Mutex and sync.RWMutex types and are assigned a globally unique
integer ID. The safe.Lock and safe.RLock methods sort the mutexes
by this integer ID before locking to ensure that locks for a given
set of mutexes are always performed in the same order, avoiding
deadlocks.

internal/bridge/configure.go

@@ -64,5 +64,5 @@ func (bridge *Bridge) ConfigureAppleMail(userID, address string) error {
 			addresses,
 			user.BridgePass(),
 		)
-	}, &bridge.usersLock)
+	}, bridge.usersLock)
 }