[mob][photos] Remove singleton pattern

mobile/lib/service_locator.dart

@@ -11,6 +11,7 @@ import "package:photos/services/machine_learning/face_ml/face_recognition_servic
 import "package:photos/services/machine_learning/machine_learning_controller.dart";
 import "package:photos/services/magic_cache_service.dart";
 import "package:photos/services/memories_cache_service.dart";
+import "package:photos/services/smart_memories_service.dart";
 import "package:photos/services/storage_bonus_service.dart";
 import "package:photos/services/trash_sync_service.dart";
 import "package:photos/services/update_service.dart";
@@ -127,6 +128,12 @@ MemoriesCacheService get memoriesCacheService {
   return _memoriesCacheService!;
 }
 
+SmartMemoriesService? _smartMemoriesService;
+SmartMemoriesService get smartMemoriesService {
+  _smartMemoriesService ??= SmartMemoriesService();
+  return _smartMemoriesService!;
+}
+
 BillingService? _billingService;
 BillingService get billingService {
   _billingService ??= BillingService(

mobile/lib/services/memories_cache_service.dart

@@ -15,7 +15,6 @@ import "package:photos/models/smart_memory.dart";
 import "package:photos/service_locator.dart";
 import "package:photos/services/location_service.dart";
 import "package:photos/services/search_service.dart";
-import "package:photos/services/smart_memories_service.dart";
 import "package:shared_preferences/shared_preferences.dart";
 
 class MemoriesCacheService {
@@ -137,9 +136,9 @@ class MemoriesCacheService {
       // calculate memories for this period and for the next period
       final now = DateTime.now();
       final next = now.add(kMemoriesUpdateFrequency);
-      final nowMemories = await SmartMemoriesService.instance.calcMemories(now);
+      final nowMemories = await smartMemoriesService.calcMemories(now);
       final nextMemories =
-          await SmartMemoriesService.instance.calcMemories(next);
+          await smartMemoriesService.calcMemories(next);
       w?.log("calculated new memories");
       final oldCache = await _readCacheFromDisk();
       w?.log("gotten old cache");

mobile/lib/services/smart_memories_service.dart

@@ -48,10 +48,7 @@ class SmartMemoriesService {
   static const _clipSimilarImageThreshold = 0.75;
   static const _clipActivityQueryThreshold = 0.25;
 
-  // Singleton pattern
-  SmartMemoriesService._privateConstructor();
-  static final instance = SmartMemoriesService._privateConstructor();
-  factory SmartMemoriesService() => instance;
+  SmartMemoriesService();
 
   Future<void> init() async {
     if (_isInit) return;