[BUG][Java][x-implements] Generated inner-`enum` lack `implements`

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• 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

Inner enums lack implements, while outer/standalone does not.
Discovered here: https://github.com/Chrimle/openapi-to-java-records-mustache-templates/issues/578
Same root cause as #23082

openapi-generator version

7.20.0

OpenAPI declaration file content or url

components:
  schemas:
    ExampleWithInnerEnums:
      type: object
      description: Example with inner enum class
      properties:
        exampleInner:
          type: string
          description: Example of an inner enum class
          x-implements:
            - TestInterface
          enum:
            - ENUM1
            - ENUM2
            - ENUM3

Generates:

  @JsonAdapter(ExampleInnerEnum.Adapter.class)
  public enum ExampleInnerEnum {

But should be:

  @JsonAdapter(ExampleInnerEnum.Adapter.class)
  public enum ExampleInnerEnum implements TestInterface {

Generation Details

Library: java

Steps to reproduce

Related issues/PRs

• #23082

Suggest a fix

Start by reproducing the issue with the provided OpenAPI YAML and inspect the Java generator's handling of x-implements for inner enums. Done means the generated ExampleInnerEnum declaration includes implements TestInterface, matching the expected output; compare the related issue #23082 for context.