feat(single-instance): add MacOs unix domain socket impl (#1035)

* feat(single-instance): add macos implementation

* chore(single-instance): test MacOs by adding CLI to example

* feat(single-instance): simplify macOS implementation

* chore(single-instance): address remarks

plugins/single-instance/examples/vanilla/src-tauri/tauri.conf.json

@@ -29,5 +29,17 @@
       "icons/icon.icns",
       "icons/icon.ico"
     ]
+  },
+  "plugins": {
+    "cli": {
+      "description": "Testing single-instance on MacOS",
+      "args": [
+        {
+          "name": "somearg",
+          "index": 1,
+          "takesValue": true
+        }
+      ]
+    }
   }
 }