MM-60413: Fix issues due to incorrect cache provider (#28181)

We were using a mock cache provider which mixed up LRU caches
with each other. This led to incorrect unmarshalling method calls.

We fix this by using the real cache provider.

https://mattermost.atlassian.net/browse/MM-60413

```release-note
NONE
```

server/channels/store/localcachelayer/layer_test.go

@@ -14,6 +14,7 @@ import (
 	"github.com/mattermost/mattermost/server/v8/channels/store"
 	"github.com/mattermost/mattermost/server/v8/channels/store/sqlstore"
 	"github.com/mattermost/mattermost/server/v8/channels/store/storetest"
+	"github.com/mattermost/mattermost/server/v8/platform/services/cache"
 	"golang.org/x/sync/errgroup"
 )
 
@@ -108,7 +109,7 @@ func initStores(logger mlog.LoggerIFace) {
 			if err != nil {
 				return err
 			}
-			st.Store, err = NewLocalCacheLayer(st.SqlStore, nil, nil, getMockCacheProvider(), logger)
+			st.Store, err = NewLocalCacheLayer(st.SqlStore, nil, nil, cache.NewProvider(), logger)
 			if err != nil {
 				return err
 			}

server/channels/store/localcachelayer/user_layer.go

@@ -84,8 +84,7 @@ func (s *LocalCacheUserStore) InvalidateProfilesInChannelCacheByUser(userId stri
 
 		toPass := make([]any, 0, len(keys))
 		for i := 0; i < len(keys); i++ {
-			// Note: keep https://github.com/mattermost/mattermost/pull/27830 in mind.
-			var userMap map[string]*model.User
+			var userMap model.UserMap
 			toPass = append(toPass, &userMap)
 		}
 		errs := s.rootStore.doMultiReadCache(s.rootStore.profilesInChannelCache, keys, toPass)
@@ -96,7 +95,7 @@ func (s *LocalCacheUserStore) InvalidateProfilesInChannelCacheByUser(userId stri
 				}
 				continue
 			}
-			gotMap := *(toPass[i].(*map[string]*model.User))
+			gotMap := *(toPass[i].(*model.UserMap))
 			if gotMap == nil {
 				s.rootStore.logger.Warn("Found nil userMap in InvalidateProfilesInChannelCacheByUser. This is not expected")
 				continue
@@ -147,7 +146,7 @@ func (s *LocalCacheUserStore) GetAllProfiles(options *model.UserGetOptions) ([]*
 
 func (s *LocalCacheUserStore) GetAllProfilesInChannel(ctx context.Context, channelId string, allowFromCache bool) (map[string]*model.User, error) {
 	if allowFromCache {
-		var cachedMap map[string]*model.User
+		var cachedMap model.UserMap
 		if err := s.rootStore.doStandardReadCache(s.rootStore.profilesInChannelCache, channelId, &cachedMap); err == nil {
 			return cachedMap, nil
 		}