Add support for nested virtualization for Windows (WSL2 / Hyper-V)

[lhotari]

I wanted to test Hyper-V virtualization for a cross-platform AI agent sandboxing solution and couldn't get Windows 11 to boot after enabling Hyper-V.

I did have /sys/module/kvm_intel/parameters/nested enabled by default. After trial and error, I found out that certain cpu flag changes are needed. It's able to boot after adding "-hypervisor".

However, after many attempts, I didn't get things working with quickemu and switched to libvirt.
Here's the guide for installing Windows with quickemu and then migrating to libvirt. WSL2 works fine now.
https://gist.github.com/lhotari/907e903f3360af340aac42b2f3c458ea