Remove flutter chat (#26)

Had to squash merge manually as Forgejo was erroring

lib/models/ms_duration.dart

@@ -0,0 +1,11 @@
+import "package:freezed_annotation/freezed_annotation.dart";
+
+class MSDuration implements JsonConverter<Duration, int> {
+  const MSDuration();
+
+  @override
+  Duration fromJson(int ms) => Duration(milliseconds: ms);
+
+  @override
+  int toJson(Duration duration) => duration.inMilliseconds;
+}