virtio: update core queue to have separate work and completion types

[Brian-Perkins]

In preparation for adding the packed queue type, update how work is fetched and completed from a queue. Additionally, isolate split queue specific logic.

[github-actions]

⚠️ Unsafe Code Detected

This PR modifies files containing unsafe Rust code. Extra scrutiny is required during review.

For more on why we check whole files, instead of just diffs, check out the Rustonomicon

[Copilot]

Pull request overview

This PR refactors the virtio queue implementation to separate work fetching (reading from available ring) from work completion (writing to used ring), preparing the codebase for future packed queue support. The refactoring isolates split queue-specific logic and introduces cleaner abstractions.

Changes:

• Split QueueCore into QueueCoreGetWork and QueueCoreCompleteWork to separate read and write operations
• Introduced QueueWork, QueueCompletionContext, and QueueDescriptor types to encapsulate queue work and completion state
• Renamed Descriptor to SplitDescriptor to distinguish split queue format from future packed queue format
• Added power-of-2 validation for queue sizes and added VIRTIO_F_VERSION_1 feature flag support
• Updated tests to use valid queue sizes (changed from 5 to 8 to satisfy power-of-2 requirement)

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
vm/devices/virtio/virtio/src/queue.rs	Core refactoring: split queue operations into get/complete, added new types, isolated split queue logic
vm/devices/virtio/virtio/src/common.rs	Updated to use new split queue APIs, modified work completion flow
vm/devices/virtio/virtio/src/spec.rs	Renamed Descriptor to SplitDescriptor for clarity
vm/devices/virtio/virtio/src/tests.rs	Added indirect descriptor feature flag, fixed queue sizes to be power-of-2

[github-actions]

At least one Petri test failed.

[Brian-Perkins]

The unsafe blocks are in the tests.rs module so not part of production.