Add "cross-emulation" support

[albertofaria]

When combined with --emulated, this enables running VMs with an architecture different from the host's.

Closes #62.

TODO

• [ ] Wait for #54 to be merged.
• [ ] Wait for BZ#2279710 to be resolved and virt-inspector in Fedora 40 to work under a user namespace.

[albertofaria]

cc @ericcurtin

[ericcurtin]

I don't know Rust well yet, just C, C++ of those kinds of languages.

But, I'll leave a few comments, regard all comments optional.

[ericcurtin]

Looks great to me in general though...