service: add unit tests for LCOW v2 shim service layer

Add unit tests for the sandbox, shimdiag, and task service methods in
cmd/containerd-shim-lcow-v2/service/. Tests exercise the public TTRPC
methods directly — including the instrumentation layer — with a mocked
vm.Controller injected via export_test.go.

The mock is generated from the vm.Controller interface using mockgen and
lives at internal/controller/vm/mock/mock_vm.go. A go:generate directive
is added to internal/controller/vm/interface.go.

14 test functions, 57 subtests covering: sandbox ID mismatch guards across
7 methods, duplicate sandbox rejection, missing config.json, StartVM
success and failure, platform state gating, StopSandbox terminate paths,
WaitSandbox exit code mapping (clean vs ERROR_INTERNAL_ERROR) and Wait/
ExitStatus failures, SandboxStatus for all 5 VM states plus ExitStatus
error, ShutdownSandbox terminate-error-swallowing, SandboxMetrics marshal
roundtrip, DiagExecInHost delegation, DiagPid, and ErrNotImplemented
coverage for all 20 stub methods.

Not covered: the full CreateSandbox -> BuildSandboxConfig -> CreateVM path
(BuildSandboxConfig has its own tests in internal/builder/vm/lcow/) and
the confidential StartSandbox path (reads boot files from disk — belongs
in functional tests).

All tests run without admin privileges or HCS.

Signed-off-by: Shreyansh Sancheti <shsancheti@microsoft.com>

Author: Shreyansh Sancheti

cmd/containerd-shim-lcow-v2/service/export_test.go

@@ -0,0 +1,26 @@
+//go:build windows
+
+package service
+
+import (
+	"github.com/Microsoft/hcsshim/internal/builder/vm/lcow"
+	"github.com/Microsoft/hcsshim/internal/controller/vm"
+
+	"github.com/containerd/containerd/v2/pkg/shutdown"
+)
+
+func SetSandboxIDForTest(s *Service, id string) {
+	s.sandboxID = id
+}
+
+func SetSandboxOptionsForTest(s *Service, opts *lcow.SandboxOptions) {
+	s.sandboxOptions = opts
+}
+
+func NewTestService(ctrl vm.Controller, sd shutdown.Service) *Service {
+	return &Service{
+		vmController: ctrl,
+		events:       make(chan interface{}, 128),
+		shutdown:     sd,
+	}
+}