add matrix: URI deeplinking

Fixes #148

Needs cross-platform testing, currently only tested on Android.

lib/controllers/link_request.dart

@@ -0,0 +1,21 @@
+import "package:app_links/app_links.dart";
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:nexus/helpers/extensions/get_link_info.dart";
+
+class LinkRequestController extends Notifier<LinkInfo?> {
+  @override
+  LinkInfo? build() {
+    final subscription = AppLinks().uriLinkStream.listen((uri) {
+      if (uri.toString().linkInfo case final linkInfo?) state = linkInfo;
+    });
+    ref.onDispose(subscription.cancel);
+
+    return null;
+  }
+
+  void consume() => state = null;
+
+  static final provider = NotifierProvider<LinkRequestController, LinkInfo?>(
+    LinkRequestController.new,
+  );
+}