[Feature request] compute support

**Describe the solution you'd like**
I'm using freezed in the example but in the background that is using this package.

I would like to have generated option for json serialization via isolates.

So that this:
```dart
@freezed
class DisbursementEntity with _$DisbursementEntity {
const factory DisbursementEntity({
required String asset,
required String disbursementPlatformDomain,
required String organizationName,
required String signature,
}) = _DisbursementEntity;

static Future fromJsonStringCompute(
String jsonString,
) async {
final result = await compute(
(jsonString) => DisbursementEntity.fromJson(jsonDecode(jsonString)),
jsonString,
);
return result;
}

factory DisbursementEntity.fromJson(Map json) =>
_$DisbursementEntityFromJson(json);
}

extension DisbursementEntityX on DisbursementEntity {
Future toJsonStringCompute() async {
final result = await compute(
(disbursement) => jsonEncode(disbursement.toJson()),
this,
);
return result;
}
}
```

Can become this:
```dart
@freezed
class DisbursementEntity with _$DisbursementEntity {
const factory DisbursementEntity({
required String asset,
required String disbursementPlatformDomain,
required String organizationName,
required String signature,
}) = _DisbursementEntity;

static Future fromJsonStringCompute(String json) =>
_$DisbursementEntityFromJsonStringCompute(json);

factory DisbursementEntity.fromJson(Map json) =>
_$DisbursementEntityFromJson(json);
}
```