mariadb backup: a RestoreJob restores the newest dump in the prefix, whichever Backup it names #5196

Describe the bug

A RestoreJob that names a MariaDB Backup does not restore the dump of that Backup. The driver creates k8s.mariadb.com/Restore with backupRef set to the operator Backup and no targetRecoveryTime, mariadb-operator takes the storage settings from that Backup and restores the newest backup.<timestamp>.<alg>.sql it finds in the prefix before the restore started. With the default strategy every backup of an app shares the prefix <namespace>/<app>/, so any RestoreJob restores the latest dump.

Environment

Cozystack v1.7.0, mariadb-operator 25.10.2.

To reproduce

1. MariaDB app m1 with row 1, run BackupJob A.
2. Insert row 2, run BackupJob B.
3. Create a RestoreJob with backupRef: <A> into an empty second MariaDB app (to-copy).

Actual behaviour

The second app has rows 1 and 2. The operator Restore pod log:

{"msg":"obtained target time","time":"2026-11-04 08:48:46 +0000 UTC"}
{"msg":"obtained target backup","file":"<namespace>/m1/backup.2026-11-04T08:47:17Z.gzip.sql"}

That is the dump of B (08:47:17), the dump of A was taken 08:46:43. Same when the dump of A is already gone: RestoreJob from A still ends Succeeded and restores the newer dump.

Expected behaviour

Restore uses the dump of the Backup it names, or fails when that dump is gone.

I think the driver has to resolve the dump that belongs to the operator Backup and pass its timestamp as targetRecoveryTime, or use a prefix per Backup. #3549 is about restore options in general, not this.