Add flutter_lints and fix analyzer errors, dead code, and unused imports

lib/models/direction_fov.dart

@@ -9,7 +9,7 @@ class DirectionFov {
   DirectionFov(this.centerDegrees, this.fovDegrees);
   
   @override
-  String toString() => 'DirectionFov(center: ${centerDegrees}°, fov: ${fovDegrees}°)';
+  String toString() => 'DirectionFov(center: $centerDegrees°, fov: $fovDegrees°)';
   
   @override
   bool operator ==(Object other) =>

lib/models/node_profile.dart

@@ -1,4 +1,3 @@
-import 'package:uuid/uuid.dart';
 import 'osm_node.dart';
 
 /// Sentinel value for copyWith methods to distinguish between null and not provided

lib/models/operator_profile.dart

@@ -1,4 +1,3 @@
-import 'package:uuid/uuid.dart';
 import 'osm_node.dart';
 
 /// A bundle of OSM tags that describe a particular surveillance operator.