Implement Virtual Machine Lifecycle Management

[jjl9807]

This PR brings the following changes:

• Introduce Machine struct in machine.rs to represent a virtual machine, including methods for initialization, spawning, and command execution.
• Implement QEMU process management in qemu.rs, including launching and logging output.
• Create SSH handling in ssh.rs, allowing for command execution and connection management via vsock.
• Add utility functions in utils.rs for directory management and prerequisite checks.
• Ensure proper cleanup of resources upon machine shutdown and drop.

[genedna]

@codex review

[Copilot]

Pull request overview

This PR implements a comprehensive virtual machine lifecycle management system using QEMU with SSH connectivity via vsock. The implementation includes image downloading and caching, cloud-init configuration for VM initialization, and proper resource cleanup.

Key Changes:

• Machine struct with initialization, spawning, execution, and shutdown methods
• QEMU process management with timeout handling and output logging
• SSH connection handling over vsock with cancellation token support

Reviewed changes

Copilot reviewed 9 out of 12 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
Cargo.toml	Defines package metadata and dependencies for the qlean project
src/lib.rs	Provides the public API with with_machine helper function
src/machine.rs	Core machine lifecycle implementation including initialization, spawning, execution, and cleanup
src/qemu.rs	QEMU process launching and management with output capture
src/ssh.rs	SSH key generation, connection management, and command execution over vsock
src/utils.rs	Utility functions for directory management, CID allocation, and prerequisite checks
src/image.rs	Image downloading, checksum verification, and kernel/initrd extraction
tests/single_machine.rs	Integration test demonstrating basic VM usage
.github/workflows/check-and-test.yml	CI workflow for format, clippy, and test checks

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