Further refactor pointOnFeature to use library functions for area and length calculations

Author: Newmanjack

lib/src/point_on_feature.dart

@@ -3,6 +3,8 @@ import 'package:geotypes/geotypes.dart';
 import 'package:turf/centroid.dart';
 import 'package:turf/boolean.dart';
 import 'package:turf/midpoint.dart';
+import 'package:turf/area.dart';
+import 'package:turf/length.dart';
 
 /// Returns a [Feature<Point>] that represents a point guaranteed to be on the feature.
 ///
@@ -111,40 +113,14 @@ double _calculateFeatureSize(Feature feature) {
     return 0; // Points have zero area
   } else if (geometry is LineString) {
     // For LineString, use the length as a proxy for size
-    double totalLength = 0;
-    final coords = geometry.coordinates;
-    for (int i = 0; i < coords.length - 1; i++) {
-      final start = coords[i];
-      final end = coords[i + 1];
-      final dx = (end[0] ?? 0.0) - (start[0] ?? 0.0);
-      final dy = (end[1] ?? 0.0) - (start[1] ?? 0.0);
-      totalLength += math.sqrt(dx * dx + dy * dy); // Simple Euclidean distance
-    }
-    return totalLength;
+    // Use the built-in length function that accounts for geodesic distance
+    return length(Feature<LineString>(geometry: geometry)).toDouble();
   } else if (geometry is Polygon) {
-    // For Polygon, use area of the outer ring as a simple approximation
-    double area = 0;
-    final outerRing = geometry.coordinates.first;
-    for (int i = 0; i < outerRing.length - 1; i++) {
-      area += ((outerRing[i][0] ?? 0.0) * (outerRing[i + 1][1] ?? 0.0)) - 
-              ((outerRing[i + 1][0] ?? 0.0) * (outerRing[i][1] ?? 0.0));
-    }
-    return area.abs() / 2;
+    // For Polygon, use the built-in area function that uses proper spherical calculations
+    return (area(Feature<Polygon>(geometry: geometry)) ?? 0.0).toDouble();
   } else if (geometry is MultiPolygon) {
-    // For MultiPolygon, sum the areas of all polygons
-    double totalArea = 0;
-    for (final polyCoords in geometry.coordinates) {
-      if (polyCoords.isNotEmpty) {
-        final outerRing = polyCoords.first;
-        double area = 0;
-        for (int i = 0; i < outerRing.length - 1; i++) {
-          area += ((outerRing[i][0] ?? 0.0) * (outerRing[i + 1][1] ?? 0.0)) - 
-                  ((outerRing[i + 1][0] ?? 0.0) * (outerRing[i][1] ?? 0.0));
-        }
-        totalArea += area.abs() / 2;
-      }
-    }
-    return totalArea;
+    // For MultiPolygon, use the built-in area function that handles all polygons
+    return (area(Feature<MultiPolygon>(geometry: geometry)) ?? 0.0).toDouble();
   }
 
   return 0; // Default for unsupported geometry types