Add host only networking support for apple backend VMs (Apple Virtualization)

[orikad]

This feature pull request has been authored by Codex.
I have tested the feature on a macOS host on version 26.4.1 and guest macOS 26.5, and it works fine. Guest gets a host-only interface that can access the host without bridging other interfaces or NATing to the internet.
This is implemented using VZVmnetNetworkDeviceAttachment and therefore requires macOS 26+ for the host (which is checked for not breaking backwards compatbility).

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[osy]

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[orikad]

closing and reopening from a feature branch like required.