reactive_file_picker: Update freezed to version "^3.0.0"

- Bump freezed version to "^3.0.0"
- Use abstract class and regenerate the code

Author: francescoberardi

packages/reactive_file_picker/lib/multi_file.dart

@@ -4,9 +4,7 @@ import 'package:freezed_annotation/freezed_annotation.dart';
 part 'multi_file.freezed.dart';
 
 @freezed
-class MultiFile<T> with _$MultiFile<T> {
-  const MultiFile._();
-
+abstract class MultiFile<T> with _$MultiFile<T> {
   const factory MultiFile({
     @Default([]) List<T> files,
     @Default([]) List<PlatformFile> platformFiles,

packages/reactive_file_picker/lib/multi_file.freezed.dart

@@ -14,11 +14,11 @@ dependencies:
     sdk: flutter
   reactive_forms: ">=16.0.0 <18.0.0"
   file_picker: ^8.0.3
-  freezed_annotation: ^2.4.1
+  freezed_annotation: ^3.0.0
 
 dev_dependencies:
   flutter_test:
     sdk: flutter
-  freezed: ^2.5.2
+  freezed: ^3.0.0
   build_runner: ^2.4.9
   flutter_lints: ^3.0.2