[BUG] [dart-dio] Does not generate imports if the model is inherited more than once

Bug Report Checklist

• 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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

If a model has nesting greater than 1, then imports are not generated

Undefined name 'FirstMyEnumEnum'. (Documentation)

To fix this, need to add import yourself to the file my_test/lib/src/model/third.dart

import 'package:openapi/src/model/first.dart';

openapi-generator version

openapi-generator-cli 7.7.0
  commit : 4eaac3d
  built  : -999999999-01-01T00:00:00+18:00
  source : https://github.com/openapitools/openapi-generator
  docs   : https://openapi-generator.tech/

OpenAPI declaration file content or url

{
  "openapi": "3.0.3",
  "info": {
    "title": "Title",
    "description": "Title",
    "version": "1.0.0"
  },
  "servers": [
    {
      "url": "https"
    }
  ],
  "paths": {},
  "components": {
    "schemas": {
      "First": {
        "properties": {
          "my-enum": {
            "enum": [
              "first"
            ]
          }
        }
      },
      "Second": {
        "allOf": [
          {
            "$ref": "#/components/schemas/First"
          }
        ]
      },
      "Third": {
        "allOf": [
          {
            "$ref": "#/components/schemas/Second"
          }
        ]
      }
    }
  }
}

Generation Details

Steps to reproduce

java -jar openapi-generator-cli-7.8.0-20240711.071610-23.jar generate -g dart-dio -i my.json -o my_test
cd my_test
dart run build_runner build -d

Related issues/PRs

Suggest a fix

Reproduce the issue with the provided OpenAPI schema using the dart-dio generator command, then inspect the generated my_test/lib/src/model/third.dart and the generator path responsible for model imports. Run dart run build_runner build -d and confirm that the generated model includes the needed import and no longer reports the undefined FirstMyEnumEnum error.