libvmi: default VirtualBox access method #320

Parent

#312

What to build

With no access method init data, LibVMI asks libmicrovmi for the default (VBoxVMI at the default socket, else MachineDebugger). Explicit VBoxVMI without a socket path uses the VM's default socket. CI pin moves to the libmicrovmi dev commit that has the default and the vCPU count export.

Acceptance criteria

• No init data + VBoxVMI enabled → VBoxVMI used (libmicrovmi info log)
• No init data + VBoxVMI disabled → MachineDebugger used
• Explicit VBoxVMI without path → default socket
• Explicit socket path that does not exist → vmi_init fails
• CI pinned to the new dev commit and green