fix(openapi3): anyOf with $ref + inline object incorrectly imported as model instead of union

[Copilot]

When anyOf contains a $ref alongside an inline object schema, the importer was discarding the $ref variant and emitting only a model from the object — losing the union semantics entirely.

Root cause: getTypeSpecKind and unwrapSingleAnyOfOneOf filtered out $ref members when counting "meaningful inline members". With exactly one inline object remaining, they concluded the schema was a plain model, never checking whether $ref members were also present as union variants.

Fix:

• Both functions now check hasRefMembers before applying the single-inline-object → model shortcut
• If any $ref members exist alongside the inline object, the schema is correctly classified as a union

# Input — was producing `model VoiceIdsOrCustomVoice { id: string }`
VoiceIdsOrCustomVoice:
  anyOf:
    - $ref: '#/components/schemas/VoiceIdsShared'
    - type: object
      properties:
        id: { type: string }

// Now correctly produces:
union VoiceIdsOrCustomVoice {
  VoiceIdsShared,
  { id: string },
}

The single-inline-object → model unwrap still applies when no $ref members are present (e.g. anyOf: [{type: object, ...}, {type: null}]), preserving existing behavior.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>import tool - composition of object + enum not handled correctly</issue_title>
<issue_description>The following OpenAPI description

components:
  schemas:
    VoiceIdsOrCustomVoice:
      title: Voice
      description: |
        A built-in voice name or a custom voice reference.
      anyOf:
        - $ref: '#/components/schemas/VoiceIdsShared'
        - type: object
          description: Custom voice reference.
          additionalProperties: false
          required:
            - id
          properties:
            id:
              type: string
    VoiceIdsShared:
      example: ash
      anyOf:
        - type: string
        - type: string
          enum:
            - alloy
            - ash
            - ballad
            - coral
            - echo
            - sage
            - shimmer
            - verse
            - marin
            - cedar

Results in the following TypeSpec definition after import

/** Custom voice reference. */
@summary("Voice")
model VoiceIdsOrCustomVoice {
  /** The custom voice ID, e.g. `voice_1234`. */
  id: string;
}

union VoiceIdsShared {
  string,

    | "alloy"
    | "ash"
    | "ballad"
    | "coral"
    | "echo"
    | "sage"
    | "shimmer"
    | "verse"
    | "marin"
    | "cedar",
}

But should really be

/** Custom voice reference. */
@summary("Voice")
union VoiceIdsOrCustomVoice {
  VoiceIdsShared,
  {
    id: string,
  },
}

union VoiceIdsShared {
  string,

    | "alloy"
    | "ash"
    | "ballad"
    | "coral"
    | "echo"
    | "sage"
    | "shimmer"
    | "verse"
    | "marin"
    | "cedar",
}

Interestingly enough, the following input OpenAPI description works as expected even though it's more complex.

components:
  schemas:
    VoiceIdsOrCustomVoice:
      title: Voice
      description: |
        A built-in voice name or a custom voice reference.
      anyOf:
        - allOf:
            - $ref: '#/components/schemas/VoiceIdsShared'
          type: string
        - type: object
          description: Custom voice reference.
          additionalProperties: false
          required:
            - id
          properties:
            id:
              type: string
    VoiceIdsShared:
      example: ash
      anyOf:
        - type: string
        - type: string
          enum:
            - alloy
            - ash
            - ballad
            - coral
            - echo
            - sage
            - shimmer
            - verse
            - marin
            - cedar
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes import tool - composition of object + enum not handled correctly #10040

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