Add notification post-livemigration

[jaykrell]

This pull request adds a notification post-livemigration.
Guests are not generally meant to be aware of live migration, but there are or soon will be exceptions, and this will support them.

[Copilot]

Pull request overview

This pull request adds support for post-live-migration notifications in the Guest Emulation Transport (GET) protocol. It introduces a new guest notification type that will allow the host to notify the guest when a live migration has completed, enabling the guest to take appropriate actions in response.

Changes:

• Adds NOTIFY_POST_LIVE_MIGRATION guest notification to the GET protocol
• Implements callback infrastructure for handling post-live-migration notifications
• Integrates the notification callback setup in OpenHCL worker initialization

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 10 comments.

File	Description
vm/devices/get/get_protocol/src/lib.rs	Defines new NOTIFY_POST_LIVE_MIGRATION guest notification constant
vm/devices/get/guest_emulation_transport/src/process_loop.rs	Adds message type, field storage, and notification handling for post-live-migration callback
vm/devices/get/guest_emulation_transport/src/client.rs	Adds public API method to set the post-live-migration notification callback
openhcl/underhill_core/src/worker.rs	Attempts to wire up the callback in OpenHCL initialization

[github-actions]

At least one Petri test failed.