GCS (Guest Compute Service) bridge for Windows Hyper-V utility VMs.
Host-side library that connects to a running UVM's in-guest GCS over an
hvsock (Hyper-V virtual socket), negotiates the GCS protocol, and
dispatches RPCs (CreateContainer, ExecuteProcess, ModifySettings, ...).
Mirrors hcsshim's internal/gcs/{guestconnection.go, container.go, prot/protocol.go} Go reference implementation.
All FFI sits behind #[cfg(target_os = "windows")] — the crate compiles
cleanly on non-Windows hosts (with the public types stubbed) so the rest
of the workspace stays buildable on Linux/macOS dev boxes.