test(cli): verify closed log files portably on Windows

Use Write rather than Stat to verify retained file handles are closed.
Windows Stat returns ERROR_INVALID_HANDLE instead of os.ErrClosed.
Retain final-cleanup content assertions and strict closed-error matching.

cmd/cli/internal_log_shutdown_test.go

@@ -36,7 +36,7 @@ func TestFinishRunClosesInternalFilesWithoutServiceStop(t *testing.T) {
 	close(p.runDone)
 	p.finishRun()
 	for i, f := range files {
-		if _, err := f.Stat(); !errors.Is(err, os.ErrClosed) {
+		if _, err := f.Write([]byte("unexpected write\n")); !errors.Is(err, os.ErrClosed) {
 			t.Errorf("file %d is not closed: %v", i, err)
 		}
 		b, err := os.ReadFile(paths[i])