fix(vmrestore): drop usb devices in best effort clone

[danilrwx]

Description

Fix VM clone behavior in BestEffort mode when source VM has attached USB devices.

The restore handler now filters out spec.usbDevices during clone validation for SnapshotOperationModeBestEffort, so clone creation is not blocked by USB dependencies.

Also extended unit tests in vm_restorer_test.go to verify:

• USB devices are removed in BestEffort mode
• USB devices are preserved in Strict mode

Why do we need it, and what problem does it solve?

In BestEffort clone mode, we should tolerate dependencies that cannot be reproduced in the clone target.

USB devices may be busy or attached to another VM, and carrying them over to a cloned VM can cause clone failures or invalid restore behavior. This change makes BestEffort clone semantics consistent by dropping USB attachments from the cloned VM spec.

What is the expected result?

1. Create a VM with spec.usbDevices.
2. Run clone/restore in BestEffort mode.
3. Verify the cloned VM is created successfully and has no spec.usbDevices.
4. Run clone/restore in Strict mode.
5. Verify spec.usbDevices are kept in the cloned VM.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: core
type: fix
summary: Drop usb devices from VM clone spec in best effort restore mode.
impact_level: low