catch and correct possible bad values for lat/lon, add tests

test/services/coordinate_validation_test.dart

@@ -0,0 +1,56 @@
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:deflockapp/services/coordinate_validation.dart';
+
+void main() {
+  group('isValidCoordinate', () {
+    test('accepts normal in-range values', () {
+      expect(isValidCoordinate(0), isTrue);
+      expect(isValidCoordinate(37.7749), isTrue);
+      expect(isValidCoordinate(-122.4194), isTrue);
+      expect(isValidCoordinate(180), isTrue);
+      expect(isValidCoordinate(-180), isTrue);
+    });
+
+    test('rejects NaN', () {
+      expect(isValidCoordinate(double.nan), isFalse);
+    });
+
+    test('rejects positive and negative infinity', () {
+      expect(isValidCoordinate(double.infinity), isFalse);
+      expect(isValidCoordinate(double.negativeInfinity), isFalse);
+    });
+
+    test('rejects out-of-range values', () {
+      expect(isValidCoordinate(180.1), isFalse);
+      expect(isValidCoordinate(-180.1), isFalse);
+      expect(isValidCoordinate(1000), isFalse);
+    });
+  });
+
+  group('isValidZoom', () {
+    test('accepts normal in-range values', () {
+      expect(isValidZoom(0), isTrue);
+      expect(isValidZoom(15), isTrue);
+      expect(isValidZoom(25), isTrue);
+    });
+
+    test('rejects NaN and Infinite', () {
+      expect(isValidZoom(double.nan), isFalse);
+      expect(isValidZoom(double.infinity), isFalse);
+      expect(isValidZoom(double.negativeInfinity), isFalse);
+    });
+
+    test('rejects out-of-range values with default bounds', () {
+      expect(isValidZoom(-1), isFalse);
+      expect(isValidZoom(26), isFalse);
+    });
+
+    test('respects custom min/max bounds', () {
+      expect(isValidZoom(0.5, min: 1.0, max: 20.0), isFalse);
+      expect(isValidZoom(1.0, min: 1.0, max: 20.0), isTrue);
+      expect(isValidZoom(20.0, min: 1.0, max: 20.0), isTrue);
+      expect(isValidZoom(20.1, min: 1.0, max: 20.0), isFalse);
+    });
+  });
+}