Fix hyperlight shutdown mechanism to prevent error spam

[danbugs]

Currently hyperlight shutdown produces multiple ERROR messages about GuestAborted and broken pipes that confuse users. Need to implement proper graceful shutdown that doesn't flood logs with expected shutdown errors when guest execution completes normally.

ERROR [hyperlight_host::sandbox::outb] error=GuestAborted(32, "")
ERROR [hyperlight_host::hypervisor::kvm] error=GuestAborted(32, "")
ERROR [hyperlight_host::hypervisor] error=GuestAborted(32, "")
ERROR [hyperlight_host::hypervisor::kvm] error=GuestAborted(32, "")
ERROR [hyperlight_host::sandbox::uninitialized_evolve] error=GuestAborted(32, "")
ERROR [hyperlight_host::sandbox::uninitialized_evolve] error=GuestAborted(32, "")
ERROR [hyperlight_host::sandbox::uninitialized] error=GuestAborted(32, "")
INFO [uservm::orchestrator] try_receive_from_vcpu(): vCPU shutdown
ERROR [syscomm::socket_stream] write_all(): write_all(): Broken pipe (os error 32)
WARN [nanvix_sandbox::single_process::uservm] shutdown(): failed to send shutdown command to user VM (error=Os { code: 32, kind: BrokenPipe, message: "Broken pipe" })