feat: add QMP lifecycle control and narrow public API (#21)

- Integrate QMP for graceful VM shutdown and running-state queries.
- Make SSH launch timeout configurable and support ephemeral images via auto-cleanup.
- Add builder-style chaining for `ImageConfig` and `MachineConfig`.
- Tighten the public API surface and align doc comments with rustdoc conventions.

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

feat: introduce machine pool with integrated network setup (#8)

* feat: introduce machine pool with integrated network setup

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* chore: bump version to 0.2.0

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* docs: update README with multi-machine usage documentation

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* docs: update README with network configuration

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* feat: enhance Machine methods to track remote IP and process status

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* feat: add validation to prevent duplicate names in MachinePool

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* fix: improve network management in `ensure_network` function

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

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Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

feat: add SFTP file transfer and `std::fs`-compatible operations (#4)

* fix: correct spelling errors

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* fix: improve error handling for SSH connection timeout

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* feat: add file transfer capabilities via SFTP

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* feat: add `std::fs`-compatible file operations

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* feat: add test cases for file operations

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* docs: add README and update package metadata

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

* fix: enhance symlink support and improve error handling

Signed-off-by: jl.jiang <jiangjl9807@gmail.com>

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Signed-off-by: jl.jiang <jiangjl9807@gmail.com>