Make the --hypervisor argument optional for the build and tests
commands. Add detect_hypervisor_device() and resolve_hypervisor_device()
helpers that map an explicit kvm/mshv name to its device node, or fall
back to probing /dev/mshv and /dev/kvm on the host when the flag is
omitted. The resolved device is validated before it is mounted into the
container, and an explicit --hypervisor is still forwarded to the test
scripts.
Assisted-by: Claude:Opus-4.8
Signed-off-by: Muminul Islam <muislam@microsoft.com>