refactor: Make support for file storing optional in database API

lib/src/database/database.dart

@@ -75,6 +75,9 @@ class Database extends _$Database implements DatabaseApi {
 
   Database.connect(DatabaseConnection connection) : super.connect(connection);
 
+  @override
+  bool get supportsFileStoring => true;
+
   @override
   int get schemaVersion => 12;
 

lib/src/database/database_api.dart

@@ -28,6 +28,7 @@ import '../../famedlysdk.dart';
 
 abstract class DatabaseApi {
   int get maxFileSize => 1 * 1024 * 1024;
+  bool get supportsFileStoring => false;
   Future<Map<String, dynamic>> getClient(String name);
 
   Future updateClient(

test/client_test.dart

@@ -590,7 +590,8 @@ void main() {
       final client = await getClient();
       final response = await client.uploadContent(Uint8List(0), 'file.jpeg');
       expect(response, 'mxc://example.com/AQwafuaFswefuhsfAFAgsw');
-      expect(await client.database.getFile(response) != null, true);
+      expect(await client.database.getFile(response) != null,
+          client.database.supportsFileStoring);
       await client.dispose(closeDatabase: true);
     });
 

test/event_test.dart

@@ -1263,13 +1263,15 @@ void main() {
       expect(await event.isAttachmentInLocalStore(), false);
       var buffer = await event.downloadAndDecryptAttachment(
           downloadCallback: downloadCallback);
-      expect(await event.isAttachmentInLocalStore(), true);
+      expect(await event.isAttachmentInLocalStore(),
+          event.room.client.database.supportsFileStoring);
       expect(buffer.bytes, FILE_BUFF);
       expect(serverHits, 1);
       buffer = await event.downloadAndDecryptAttachment(
           downloadCallback: downloadCallback);
       expect(buffer.bytes, FILE_BUFF);
-      expect(serverHits, 1);
+      expect(
+          serverHits, event.room.client.database.supportsFileStoring ? 1 : 2);
 
       await room.client.dispose(closeDatabase: true);
     });