Fix mixed units assemblies to work, regardless of project settings (#5818)

* Add mixed units test

* Add incorrect output

* Change to always set units since old units are not accurate

* Update output after fix

rust/kcl-lib/tests/kcl_samples/router-template-slate/artifact_commands.snap

@@ -53,6 +53,18 @@ description: Artifact commands router-template-slate.kcl
       "hidden": true
     }
   },
+  {
+    "cmdId": "[uuid]",
+    "range": [
+      93,
+      126,
+      0
+    ],
+    "command": {
+      "type": "set_scene_units",
+      "unit": "mm"
+    }
+  },
   {
     "cmdId": "[uuid]",
     "range": [