[RefactoredBMS] Ensure backup doesn't reuse ack tokens nearby in time

This CL replicates both ag/2551800 and ag/2613950 in RefactoredBMS.

Test: runtest -p com.android.server.backup frameworks-services
Bug: 37973765
Change-Id: I5e42dee67d587adabbfb81de03f3205d92a46add