Update the pubspec dependency for protobuf to at least 4.0.0

[dominikmucklow]

Request to update the pubspec dependency for protobuf to at least 4.0.0. The current dependency of 3.1.0 causes compilation failures when other packages rely on newer versions of protobuf.

[dominikmucklow]

@wenkaifan0720 are there plans to update the protobuf dependency for this repository? Ever since the update to Flutter 3.32.4 I have run into compilation failures in FlutterFlow due to conflicts with other packages.