refactor: Make direct chat getter type safe

This also makes sure that we
do not accidentally change
it in RAM before the
change comes from the server
when calling
addToDirectChat()

lib/src/client.dart

@@ -442,8 +442,13 @@ class Client extends MatrixApi {
     return null;
   }
 
-  Map<String, dynamic> get directChats =>
-      _accountData['m.direct']?.content ?? {};
+  Map<String, List<String>> get directChats =>
+      (_accountData['m.direct']?.content ?? {}).map(
+        (userId, list) => MapEntry(
+          userId,
+          (list is! List) ? [] : list.whereType<String>().toList(),
+        ),
+      );
 
   /// Returns the (first) room ID from the store which is a private chat with the user [userId].
   /// Returns null if there is none.

lib/src/room.dart

@@ -344,7 +344,7 @@ class Room {
     final cache = _cachedDirectChatMatrixId;
     if (cache != null) {
       final roomIds = client.directChats[cache];
-      if (roomIds is List && roomIds.contains(id)) {
+      if (roomIds != null && roomIds.contains(id)) {
         return cache;
       }
     }
@@ -1372,21 +1372,21 @@ class Room {
 
   /// Sets this room as a direct chat for this user if not already.
   Future<void> addToDirectChat(String userID) async {
-    final directChats = client.directChats;
-    if (directChats[userID] is List) {
-      if (!directChats[userID].contains(id)) {
-        directChats[userID].add(id);
-      } else {
-        return;
-      } // Is already in direct chats
-    } else {
-      directChats[userID] = [id];
+    final dmRooms = List<String>.from(client.directChats[userID] ?? []);
+    if (dmRooms.contains(id)) {
+      Logs().d('Already a direct chat.');
+      return;
     }
 
+    dmRooms.add(id);
+
     await client.setAccountData(
       client.userID!,
       'm.direct',
-      directChats,
+      {
+        ...client.directChats,
+        userID: dmRooms,
+      },
     );
     return;
   }