Move to Flutter 3.47, use the improvements that come with this (#64)

Reviewed-on: #64

lib/models/info/audio.dart

@@ -1,16 +1,17 @@
 import "package:freezed_annotation/freezed_annotation.dart";
 import "package:nexus/models/ms_duration.dart";
+
 part "audio.freezed.dart";
 part "audio.g.dart";
 
-@freezed
-abstract class AudioInfo with _$AudioInfo {
-  /// Information for images, [size] is in bytes.
-  const factory AudioInfo({
-    @MSDuration() Duration? duration,
-    @JsonKey(name: "mimetype") String? mimeType,
-    int? size,
-  }) = _AudioInfo;
+@Freezed(toJson: false, fromJson: false)
+@JsonSerializable()
+class const AudioInfo({
+  @MSDuration() final Duration? duration,
+  @JsonKey(name: "mimetype") final String? mimeType,
+  final int? size,
+}) with _$AudioInfo {
+  Map<String, Object?> toJson() => _$AudioInfoToJson(this);
 
   factory AudioInfo.fromJson(Map<String, Object?> json) =>
       _$AudioInfoFromJson(json);