Classes not being generated with new Dart 3 classes modifiers

Hi @davidmorgan, hope you are doing pretty well!

The generated code is not respecting the classes modifiers in case we mark our class with one, example:

**Entity**
```dart
abstract interface class CreateVehiclePayload {
int get year;
String get make;
String get model;
double get initialMileage;
String? get plate;
String? get plateState;
String? get vin;

String toJson();
}
```

**Model**
```dart
library create_vehicle_payload_model;

part 'create_vehicle_payload_model.g.dart';

abstract final class CreateVehiclePayloadModel
implements CreateVehiclePayload, Built {
const CreateVehiclePayloadModel._();

factory CreateVehiclePayloadModel({
required int year,
required String model,
required String make,
required double initialMileage,
String? plate,
String? plateState,
String? vin,
}) =>
_$CreateVehiclePayloadModel(
(b) => b
..year = year
..model = model
..make = make
..initialMileage = initialMileage
..plate = plate
..vin = vin
..plateState = plateState,
);

@override
String toJson() {
return jsonEncode(coreSerializers.serializeWith(CreateVehiclePayloadModel.serializer, this));
}

static Serializer get serializer => _$createVehiclePayloadModelSerializer;
}
```

Then, if I run the command `flutter pub run build_runner build --delete-conflicting-outputs`, I get the following generated file:

```dart
// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'create_vehicle_payload_model.dart';

// **************************************************************************
// BuiltValueGenerator
// **************************************************************************

Serializer _$createVehiclePayloadModelSerializer =
new _$CreateVehiclePayloadModelSerializer();

class _$CreateVehiclePayloadModelSerializer
implements StructuredSerializer {
@override
final Iterable types = const [
CreateVehiclePayloadModel,
_$CreateVehiclePayloadModel
];
@override
final String wireName = 'CreateVehiclePayloadModel';

@override
Iterable serialize(
Serializers serializers, CreateVehiclePayloadModel object,
{FullType specifiedType = FullType.unspecified}) {
final result = [
'year',
serializers.serialize(object.year, specifiedType: const FullType(int)),
'make',
serializers.serialize(object.make, specifiedType: const FullType(String)),
'model',
serializers.serialize(object.model,
specifiedType: const FullType(String)),
'initialMileage',
serializers.serialize(object.initialMileage,
specifiedType: const FullType(double)),
];
Object? value;
value = object.plate;
if (value != null) {
result
..add('plate')
..add(serializers.serialize(value,
specifiedType: const FullType(String)));
}
value = object.plateState;
if (value != null) {
result
..add('plateState')
..add(serializers.serialize(value,
specifiedType: const FullType(String)));
}
value = object.vin;
if (value != null) {
result
..add('vin')
..add(serializers.serialize(value,
specifiedType: const FullType(String)));
}
return result;
}

@override
CreateVehiclePayloadModel deserialize(
Serializers serializers, Iterable serialized,
{FullType specifiedType = FullType.unspecified}) {
final result = new CreateVehiclePayloadModelBuilder();

final iterator = serialized.iterator;
while (iterator.moveNext()) {
final key = iterator.current! as String;
iterator.moveNext();
final Object? value = iterator.current;
switch (key) {
case 'year':
result.year = serializers.deserialize(value,
specifiedType: const FullType(int))! as int;
break;
case 'make':
result.make = serializers.deserialize(value,
specifiedType: const FullType(String))! as String;
break;
case 'model':
result.model = serializers.deserialize(value,
specifiedType: const FullType(String))! as String;
break;
case 'initialMileage':
result.initialMileage = serializers.deserialize(value,
specifiedType: const FullType(double))! as double;
break;
case 'plate':
result.plate = serializers.deserialize(value,
specifiedType: const FullType(String)) as String?;
break;
case 'plateState':
result.plateState = serializers.deserialize(value,
specifiedType: const FullType(String)) as String?;
break;
case 'vin':
result.vin = serializers.deserialize(value,
specifiedType: const FullType(String)) as String?;
break;
}
}

return result.build();
}
}

class _$CreateVehiclePayloadModel extends CreateVehiclePayloadModel {
@override
final int year;
@override
final String make;
@override
final String model;
@override
final double initialMileage;
@override
final String? plate;
@override
final String? plateState;
@override
final String? vin;

factory _$CreateVehiclePayloadModel(
[void Function(CreateVehiclePayloadModelBuilder)? updates]) =>
(new CreateVehiclePayloadModelBuilder()..update(updates))._build();

_$CreateVehiclePayloadModel._(
{required this.year,
required this.make,
required this.model,
required this.initialMileage,
this.plate,
this.plateState,
this.vin})
: super._() {
BuiltValueNullFieldError.checkNotNull(
year, r'CreateVehiclePayloadModel', 'year');
BuiltValueNullFieldError.checkNotNull(
make, r'CreateVehiclePayloadModel', 'make');
BuiltValueNullFieldError.checkNotNull(
model, r'CreateVehiclePayloadModel', 'model');
BuiltValueNullFieldError.checkNotNull(
initialMileage, r'CreateVehiclePayloadModel', 'initialMileage');
}

@override
CreateVehiclePayloadModel rebuild(
void Function(CreateVehiclePayloadModelBuilder) updates) =>
(toBuilder()..update(updates)).build();

@override
CreateVehiclePayloadModelBuilder toBuilder() =>
new CreateVehiclePayloadModelBuilder()..replace(this);

@override
bool operator ==(Object other) {
if (identical(other, this)) return true;
return other is CreateVehiclePayloadModel &&
year == other.year &&
make == other.make &&
model == other.model &&
initialMileage == other.initialMileage &&
plate == other.plate &&
plateState == other.plateState &&
vin == other.vin;
}

@override
int get hashCode {
var _$hash = 0;
_$hash = $jc(_$hash, year.hashCode);
_$hash = $jc(_$hash, make.hashCode);
_$hash = $jc(_$hash, model.hashCode);
_$hash = $jc(_$hash, initialMileage.hashCode);
_$hash = $jc(_$hash, plate.hashCode);
_$hash = $jc(_$hash, plateState.hashCode);
_$hash = $jc(_$hash, vin.hashCode);
_$hash = $jf(_$hash);
return _$hash;
}

@override
String toString() {
return (newBuiltValueToStringHelper(r'CreateVehiclePayloadModel')
..add('year', year)
..add('make', make)
..add('model', model)
..add('initialMileage', initialMileage)
..add('plate', plate)
..add('plateState', plateState)
..add('vin', vin))
.toString();
}
}

class CreateVehiclePayloadModelBuilder
implements
Builder {
_$CreateVehiclePayloadModel? _$v;

int? _year;
int? get year => _$this._year;
set year(int? year) => _$this._year = year;

String? _make;
String? get make => _$this._make;
set make(String? make) => _$this._make = make;

String? _model;
String? get model => _$this._model;
set model(String? model) => _$this._model = model;

double? _initialMileage;
double? get initialMileage => _$this._initialMileage;
set initialMileage(double? initialMileage) =>
_$this._initialMileage = initialMileage;

String? _plate;
String? get plate => _$this._plate;
set plate(String? plate) => _$this._plate = plate;

String? _plateState;
String? get plateState => _$this._plateState;
set plateState(String? plateState) => _$this._plateState = plateState;

String? _vin;
String? get vin => _$this._vin;
set vin(String? vin) => _$this._vin = vin;

CreateVehiclePayloadModelBuilder();

CreateVehiclePayloadModelBuilder get _$this {
final $v = _$v;
if ($v != null) {
_year = $v.year;
_make = $v.make;
_model = $v.model;
_initialMileage = $v.initialMileage;
_plate = $v.plate;
_plateState = $v.plateState;
_vin = $v.vin;
_$v = null;
}
return this;
}

@override
void replace(CreateVehiclePayloadModel other) {
ArgumentError.checkNotNull(other, 'other');
_$v = other as _$CreateVehiclePayloadModel;
}

@override
void update(void Function(CreateVehiclePayloadModelBuilder)? updates) {
if (updates != null) updates(this);
}

@override
CreateVehiclePayloadModel build() => _build();

_$CreateVehiclePayloadModel _build() {
final _$result = _$v ??
new _$CreateVehiclePayloadModel._(
year: BuiltValueNullFieldError.checkNotNull(
year, r'CreateVehiclePayloadModel', 'year'),
make: BuiltValueNullFieldError.checkNotNull(
make, r'CreateVehiclePayloadModel', 'make'),
model: BuiltValueNullFieldError.checkNotNull(
model, r'CreateVehiclePayloadModel', 'model'),
initialMileage: BuiltValueNullFieldError.checkNotNull(
initialMileage, r'CreateVehiclePayloadModel', 'initialMileage'),
plate: plate,
plateState: plateState,
vin: vin);
replace(_$result);
return _$result;
}
}

// ignore_for_file: deprecated_member_use_from_same_package,type=lint
```

Then I get the following error -> `The type '_$CreateVehiclePayloadModel' must be 'base', 'final' or 'sealed' because the supertype 'CreateVehiclePayloadModel' is 'final'.`. In order to make it work, I have to manually add any of the mentioned modifiers, but I think it is not ideal, adding modifiers manually for each generated class is painful.