Get machine_id working on macOS as well

tools/utils/machine_id/unix.go

@@ -0,0 +1,23 @@
+//go:build !darwin
+
+package machine_id
+
+import (
+	"fmt"
+	"os"
+	"strings"
+	"unicode"
+
+	"github.com/kovidgoyal/kitty/tools/utils"
+)
+
+var _ = fmt.Print
+
+func read_machine_id() (string, error) {
+	if data, err := os.ReadFile("/etc/machine-id"); err == nil {
+		ans := utils.UnsafeBytesToString(data)
+		return strings.TrimRightFunc(ans, unicode.IsSpace), nil
+	} else {
+		return "", err
+	}
+}