Fix a minor resource leak with display names and avatars

I noticed that calls to createDisplayNameBehavior$ and createAvatarUrlBehavior$ were technically leaking resources since they reused the ObservableScope from their outer scope, which in practice lasts for the entire lifetime of the CallViewModel. This would not have had any noticeable effect unless you had other participants leave and rejoin the same call many thousands of times.

src/state/CallViewModel/remoteMembers/MatrixMemberMetadata.ts

@@ -115,8 +115,14 @@ export const createMatrixMemberMetadata$ = (
   memberships$: Behavior<Pick<CallMembership, "userId">[]>,
   roomMembers$: Behavior<RoomMemberMap>,
 ): {
-  createDisplayNameBehavior$: (userId: string) => Behavior<string | undefined>;
-  createAvatarUrlBehavior$: (userId: string) => Behavior<string | undefined>;
+  createDisplayNameBehavior$: (
+    scope: ObservableScope,
+    userId: string,
+  ) => Behavior<string | undefined>;
+  createAvatarUrlBehavior$: (
+    scope: ObservableScope,
+    userId: string,
+  ) => Behavior<string | undefined>;
   displaynameMap$: Behavior<Map<string, string>>;
   avatarMap$: Behavior<Map<string, string | undefined>>;
 } => {
@@ -136,13 +142,13 @@ export const createMatrixMemberMetadata$ = (
     ),
   );
   return {
-    createDisplayNameBehavior$: (userId: string) =>
+    createDisplayNameBehavior$: (scope: ObservableScope, userId: string) =>
       scope.behavior(
         displaynameMap$.pipe(
           map((displaynameMap) => displaynameMap.get(userId)),
         ),
       ),
-    createAvatarUrlBehavior$: (userId: string) =>
+    createAvatarUrlBehavior$: (scope: ObservableScope, userId: string) =>
       scope.behavior(
         roomMembers$.pipe(
           map((roomMembers) => roomMembers.get(userId)?.getMxcAvatarUrl()),