[BUG][dart-dio] Using oneOf together with allOf does not generate properties

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• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

dart-dio does not generate properties for models when using oneOf together with allOf. The schema posted below generates the following code:

// ...
/// Dog
///
/// Properties:
/// * [petType] 
/// * [hunts] 
/// * [age] 
/// * [bark] 
/// * [breed] 
@BuiltValue()
abstract class Dog implements Pet, Built<Dog, DogBuilder> {
  Dog._();

  factory Dog([void updates(DogBuilder b)]) = _$Dog;

  @BuiltValueHook(initializeBuilder: true)
  static void _defaults(DogBuilder b) => b..petType=b.discriminatorValue;

  @BuiltValueSerializer(custom: true)
  static Serializer<Dog> get serializer => _$DogSerializer();
}
// ...

I'd expect that it generates all properties related to Dog (petType, bark and breed).

openapi-generator version

7.4.0

OpenAPI declaration file content or url

openapi: 3.0.1
info:
   title: pet
   version: 0.0.1
paths:
  /pets:
    patch:
      requestBody:
        content:
          application/json:
            schema:
              oneOf:
                - $ref: '#/components/schemas/Cat'
                - $ref: '#/components/schemas/Dog'
              discriminator:
                propertyName: pet_type
      responses:
        '200':
          description: Updated
components:
  schemas:
    Pet:
      type: object
      required:
        - pet_type
      properties:
        pet_type:
          type: string
      discriminator:
        propertyName: pet_type
      oneOf:
        - $ref: '#/components/schemas/Cat'
        - $ref: '#/components/schemas/Dog'
    Dog:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          properties:
            bark:
              type: boolean
            breed:
              type: string
              enum: [Dingo, Husky, Retriever, Shepherd]
    Cat:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          properties:
            hunts:
              type: boolean
            age:
              type: integer

Steps to reproduce

openapi-generator-cli generate -i pet.yaml -g dart-dio -o ./pet

Start by running the provided openapi-generator-cli command with the pet.yaml schema and inspect the dart-dio model generation for Dog. Trace how oneOf and allOf are combined, then verify that the generated Dog model includes pet_type, bark, and breed rather than only inherited interfaces.