Implement the virtio balloon statistics virtqueue per the VIRTIO spec,
exposing guest memory statistics through a new /vm.balloon-statistics
API endpoint.
Device layer: add stats virtqueue constants and types, wire up the
stats queue in the balloon handler, implement stats request/response
handlers, and expose a public request_balloon_statistics function.
VMM layer: plumb statistics through device manager, VM, and VMM,
add HTTP and D-Bus API endpoints, add ServiceUnavailable (503) to
api_client, add balloon-statistics subcommand to ch-remote, and add
the endpoint to the OpenAPI spec.
The response includes both guest-reported stats and host-known values
(balloon_actual_bytes, balloon_target_bytes, balloon_total_ram_bytes)
so consumers can understand balloon utilization without querying
/vm.info separately.
Also fixes pre-existing rustfmt issues and adds clippy+rustfmt to the
flake devShell.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Davíð Steinn Geirsson
480bfb7095