VM Snapshot stuck at Expunging with KvmFileBasedStorageVmSnapshotStrategy

### problem

`KvmFileBasedStorageVmSnapshotStrategy.deleteVMSnapshot` transitions the VM snapshot to `Expunging` during delete but doesn't transition it to `Error` state in case of exception or timeout

`VMSnapshotManagerImpl.hasActiveVMSnapshotTasks` counts `Expunging` as work in
progress, so operations like reboot and snapshot operations are blocked.

### versions

4.22

### The steps to reproduce the bug

1. Take a disk-only VM snapshot.
2. Write lots of data to the VM
3. set commands.timeout=MergeDiskOnlyVmSnapshotCommand=20
4. Delete the snapshot.

...

### What to do about it?

Snapshot state should transition to Error in case of timeout

从 KvmFileBasedStorageVmSnapshotStrategy.deleteVMSnapshot 和 VMSnapshotManagerImpl.hasActiveVMSnapshotTasks 开始，然后使用 commands.timeout=MergeDiskOnlyVmSnapshotCommand=20 重现仅磁盘快照删除。跟踪超时或异常路径，并验证快照进入 Error，而不是停留在 Expunging，从而不再阻塞重启和后续快照操作。

由索引模型根据 Issue 内容生成。