refactor: Performance boost for avatar widget

lib/widgets/presence_builder.dart

@@ -1,10 +1,12 @@
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 
 import 'package:matrix/matrix.dart';
 
 import 'package:fluffychat/widgets/matrix.dart';
 
-class PresenceBuilder extends StatelessWidget {
+class PresenceBuilder extends StatefulWidget {
   final Widget Function(BuildContext context, CachedPresence? presence) builder;
   final String? userId;
   final Client? client;
@@ -17,21 +19,41 @@ class PresenceBuilder extends StatelessWidget {
   });
 
   @override
-  Widget build(BuildContext context) {
-    final userId = this.userId;
-    if (userId == null) return builder(context, null);
-
-    final client = this.client ?? Matrix.of(context).client;
-    return FutureBuilder<CachedPresence>(
-      future: client.fetchCurrentPresence(userId),
-      builder: (context, cachedPresenceSnapshot) => StreamBuilder(
-        stream: client.onPresenceChanged.stream
-            .where((cachedPresence) => cachedPresence.userid == userId),
-        builder: (context, snapshot) => builder(
-          context,
-          snapshot.data ?? cachedPresenceSnapshot.data,
-        ),
-      ),
-    );
-  }
+  State<PresenceBuilder> createState() => _PresenceBuilderState();
+}
+
+class _PresenceBuilderState extends State<PresenceBuilder> {
+  CachedPresence? _presence;
+  StreamSubscription<CachedPresence>? _sub;
+
+  @override
+  void initState() {
+    final client = widget.client ?? Matrix.of(context).client;
+    final userId = widget.userId;
+    if (userId != null) {
+      WidgetsBinding.instance.addPostFrameCallback((_) async {
+        final presence = await client.fetchCurrentPresence(userId);
+        setState(() {
+          _presence = presence;
+          _sub = client.onPresenceChanged.stream.listen((presence) {
+            if (!mounted) return;
+            setState(() {
+              _presence = presence;
+            });
+          });
+        });
+      });
+    }
+
+    super.initState();
+  }
+
+  @override
+  void dispose() {
+    _sub?.cancel();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) => widget.builder(context, _presence);
 }