user [nfc]: Provide RealmStore to UserStore

Author: gnprice

lib/model/store.dart

@@ -495,7 +495,7 @@ class PerAccountStore extends PerAccountStoreBase with
       savedSnippets: SavedSnippetStoreImpl(core: core,
         savedSnippets: initialSnapshot.savedSnippets ?? []),
       typingNotifier: TypingNotifier(realm: realm),
-      users: UserStoreImpl(core: core, initialSnapshot: initialSnapshot),
+      users: UserStoreImpl(realm: realm, initialSnapshot: initialSnapshot),
       typingStatus: TypingStatus(realm: realm),
       presence: Presence(realm: realm,
         initial: initialSnapshot.presences),

lib/model/user.dart

@@ -4,10 +4,11 @@ import '../api/model/model.dart';
 import 'algorithms.dart';
 import 'localizations.dart';
 import 'narrow.dart';
+import 'realm.dart';
 import 'store.dart';
 
 /// The portion of [PerAccountStore] describing the users in the realm.
-mixin UserStore on PerAccountStoreBase {
+mixin UserStore on PerAccountStoreBase, RealmStore {
   /// The user with the given ID, if that user is known.
   ///
   /// There may be other users that are perfectly real but are
@@ -131,9 +132,9 @@ enum MutedUsersVisibilityEffect {
 /// Generally the only code that should need this class is [PerAccountStore]
 /// itself.  Other code accesses this functionality through [PerAccountStore],
 /// or through the mixin [UserStore] which describes its interface.
-class UserStoreImpl extends PerAccountStoreBase with UserStore {
+class UserStoreImpl extends HasRealmStore with UserStore {
   UserStoreImpl({
-    required super.core,
+    required super.realm,
     required InitialSnapshot initialSnapshot,
   }) : _users = Map.fromEntries(
          initialSnapshot.realmUsers