libmicrovmi: vCPU count in the C API #314

Parent

#312

What to build

C callers can ask a Driver for the guest's vCPU count, as Rust callers already can. Needed by LibVMI's vmi_get_num_vcpus.

Acceptance criteria

• New C export returns the vCPU count, with the same error convention as the other C exports
• Generated C header exposes it
• A C example prints the count; it shows the configured count on a VirtualBox guest over both access methods