feat: expose NavigationPage navigator observers & onPopPage

lib/src/widgets/navi_rail/yaru_navigation_page.dart

@@ -28,9 +28,11 @@ class YaruNavigationPage extends StatefulWidget {
     this.leading,
     this.trailing,
     this.navigatorKey,
+    this.navigatorObservers = const <NavigatorObserver>[],
     this.initialRoute,
     this.onGenerateRoute,
     this.onUnknownRoute,
+    this.onPopPage,
   })  : assert(initialIndex == null || controller == null),
         assert((length == null) != (controller == null));
 
@@ -67,15 +69,39 @@ class YaruNavigationPage extends StatefulWidget {
   /// A key to use when building the [Navigator] widget.
   final GlobalKey<NavigatorState>? navigatorKey;
 
+  /// The list of observers for the [Navigator] created in this page.
+  ///
+  /// See also:
+  ///  * [Navigator.observers]
+  final List<NavigatorObserver> navigatorObservers;
+
   /// The route name for the initial route.
+  ///
+  /// See also:
+  ///  * [Navigator.initialRoute]
   final String? initialRoute;
 
   /// Called to generate a route for a given [RouteSettings].
+  ///
+  /// See also:
+  ///  * [Navigator.onGenerateRoute]
   final RouteFactory? onGenerateRoute;
 
   /// Called when [onGenerateRoute] fails to generate a route.
+  ///
+  /// See also:
+  ///  * [Navigator.onUnknownRoute]
   final RouteFactory? onUnknownRoute;
 
+  /// Called when a dynamically pushed route is popped off.
+  ///
+  /// This callback is responsible for calling [Route.didPop] and returning
+  /// whether this pop is successful.
+  ///
+  /// See also:
+  ///  * [Navigator.onPopPage]
+  final PopPageCallback? onPopPage;
+
   @override
   State<YaruNavigationPage> createState() => _YaruNavigationPageState();
 }
@@ -202,8 +228,9 @@ class _YaruNavigationPageState extends State<YaruNavigationPage> {
           initialRoute: widget.initialRoute,
           onGenerateRoute: widget.onGenerateRoute,
           onUnknownRoute: widget.onUnknownRoute,
-          onPopPage: (route, result) => route.didPop(result),
-          observers: [HeroController()],
+          onPopPage: (route, result) =>
+              widget.onPopPage?.call(route, result) ?? route.didPop(result),
+          observers: [...widget.navigatorObservers, HeroController()],
         ),
       ),
     );