Dart Generator: JSON Array of Files

Hiya! Thanks for the great packages for code gen. I have a bug with the Dart generator.

Since this is a commercial project, I cannot share the entire openAPI spec, but I will attempt to share the relevant parts. We have an Order object that looks like this:

    Order:
      type: object
      properties:
        id:
          type: string
        state:
          $ref: "#/components/schemas/OrderState"
        accepted:
          type: string
          format: date
        files:
          type: array
          items:
            $ref: "#/components/schemas/File"
    File:
      type: object
      properties:
        id:
          type: string
          format: uuid
        name:
          type: string

It defines an Order object that can contain a list of File. We define our own File, but when I generate the Code, our definition isn't used, and the Files array is instead transformed into an array of MultipartFile.

Two problems:

1. The code that is generated does not compile. It attempts to call a MultipartFile.listFromJson constructor from inside the Order.fromJson method, which does not exist on the MultipartFile class.
2. This isn't what we expected to happen, but is this intentional? This is my first time generating code from a Swagger spec, but this doesn't seem intuitive. If we wanted a multipart file, I assumed we'd change the spec to look like this: https://swagger.io/docs/specification/describing-request-body/file-upload/

Happy to help address this issue, but would appreciate a bit more info from your side on whether this is "working as intended" but needs a fix for the constructor, or if it shouldn't be coerced into a different type at all.

Start in the Dart generator by locating how schema array items are mapped and how MultipartFile is selected, then compare that behavior with the Order.fromJson output described here. Done means the generated code compiles and the File schema is handled consistently with the intended OpenAPI definition, including a clear decision about multipart coercion.