Add cargo weight and draw argument support

Introduces cargo weight and draw argument properties to units across backend, frontend, and Python API. Adds related commands, data extraction, and registration logic, enabling setting and reading of cargo weight and custom draw arguments for units. Includes new API examples and updates to interfaces, data types, and Lua backend for full feature integration.

frontend/react/src/map/latlng.ts

@@ -0,0 +1,18 @@
+import * as L from "leaflet";
+
+export class LatLng extends L.LatLng {
+  threshold: number;
+  
+  constructor(lat: number, lng: number, alt: number, threshold: number) {
+    super(lat, lng, alt);
+    this.threshold = threshold;
+  }
+
+  setThreshold(threshold: number) {
+    this.threshold = threshold;
+  }
+
+  getThreshold() {
+    return this.threshold;
+  }
+}