[BUG][Rust] oneOf with array produces invalid code

[DDtKey]

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

It's nice that basic support of oneOf for rust has landed as part of #13970, but there are some issues.
It generates broken code if one of elements is "array", because it uses type-name as variant name for enum without normalization.

It leads to structures like this:

#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
#[serde(untagged)]
pub enum OneOfWithArray {
    SomeObject(Box<SomeObject>),
    Vec<crate::models::SomeObject>(Box<Vec<crate::models::SomeObject>>), // invalid rust code
}

openapi-generator version

latest master:

openapi-generator-cli 7.4.0-SNAPSHOT
  commit : 76d743b

OpenAPI declaration file content or url

Can be reproduced with existing modules/openapi-generator/src/test/resources/3_0/oneOfArrayMapImport.yaml

Or another MRE:

{
  "openapi": "3.0.3",
  "info": {
    "title": "Omitted",
    "description": "Omitted",
    "license": {
      "name": ""
    },
    "version": "0.1.0"
  },
  "servers": [
    {
      "url": "http://localhost:8080",
      "description": "Omitted"
    }
  ],
  "paths": {},
  "components": {
    "schemas": {
      "OneOfWithArray": {
        "type": "object",
        "oneOf": [
          {
            "$ref": "#/components/schemas/SomeObject"
          },
          {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/SomeObject"
            }
          }
        ]
      },
      "SomeObject": {
        "type": "object",
        "properties": {
          "a": {
            "type": "integer"
          }
        }
      }
    },
    "responses": {}
  }
}

Generation Details

Just
openapi-generator generate -i test-spec.json -g rust --package-name test-one-of --additional-properties=supportMiddleware=true -o ./test

Steps to reproduce

Just try to generate rust client for provided spec.

Related issues/PRs

#13970 - the behavior was introduced there, but it's initial version of oneOf support.

#17869 - related issue with mention of wrong String import

Suggest a fix

Instead of using type-name as enum variant name, for such cases it could be normalization. I.e replace special chars and paths, for example VecSomeObject instead of Vec<crate::models::SomeObject>(..) or even just SomeObjects. Not sure about complexity though.
And not really related to this case, but if there is a descriminator - its values can be used instead of type names

[DDtKey]

#17915 solves this and covers with tests