Fix object types with array type (e.g. ["object", "null"]) being inferred as undefined

[Copilot]

• Fix FixMissingTypeObject to not override schemas that already have a type field (e.g. type: ["object", "null"])
• Fix FixMissingAdditionalProperties to also handle schemas with array type containing "object" (e.g. type: ["object", "null"])
• Add a test OAS fixture with type: ["object", "null"] schema
• Add a TypeScript type test validating the fix
• Add changeset describing the bug fix

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Object types being inferred as undefined</issue_title>
<issue_description>Describe the bug

My openapi spec has an object type but on my fets client is showing only undefined.

To Reproduce Steps to reproduce the behavior:

Generate an openapi with this item and instantiate a fets client:

//...
"id_doc_front_file": {
    "type": [
      "object",
      "null"
    ],
    "properties": {
      "url": {
        "type": "string",
        "format": "uri",
        "example": "https://example.com/document.pdf"
      },
      "name": {
        "type": "string",
        "example": "File name.jpg"
      },
      "size": {
        "type": "number",
        "example": 123456
      }
    },
    "required": [
      "url",
      "name",
      "size"
    ]
  }
//... 

Expected behavior

It should be inferred as an object with three keys: url, name and size.

But is inferring as undefined:

Environment:

• OS: Macos Sonoma
• Openapi Version: 3.1.0
• NodeJS: 20.9.0
  </issue_description>

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

@ardatan Are you sure if it is valid to have both `object` and `null` in `type` as an array because there is always `properties` there?

• Fixes Object types being inferred as undefined #1807

---

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✅ Benchmark Results

     ✓ no_errors{server:node-http,mode:no-schema}
     ✓ expected_result{server:node-http,mode:no-schema}
     ✓ no_errors{server:node-http,mode:json-schema}
     ✓ expected_result{server:node-http,mode:json-schema}
     ✓ no_errors{server:uWebSockets,mode:no-schema}
     ✓ expected_result{server:uWebSockets,mode:no-schema}
     ✓ no_errors{server:uWebSockets,mode:json-schema}
     ✓ expected_result{server:uWebSockets,mode:json-schema}

     checks......................................: 100.00% ✓ 855566      ✗ 0     
     data_received...............................: 78 MB   647 kB/s
     data_sent...................................: 54 MB   453 kB/s
     http_req_blocked............................: avg=1.54µs   min=901ns    med=1.47µs   max=280.02µs p(90)=1.93µs   p(95)=2.09µs  
     http_req_connecting.........................: avg=1ns      min=0s       med=0s       max=124.47µs p(90)=0s       p(95)=0s      
     http_req_duration...........................: avg=197.72µs min=136.62µs med=188.24µs max=17.36ms  p(90)=214.36µs p(95)=223.19µs
       { expected_response:true }................: avg=197.72µs min=136.62µs med=188.24µs max=17.36ms  p(90)=214.36µs p(95)=223.19µs
     ✓ { server:node-http,mode:json-schema }.....: avg=210.31µs min=153.27µs med=199.63µs max=12.84ms  p(90)=223.1µs  p(95)=231.4µs 
     ✓ { server:node-http,mode:no-schema }.......: avg=203.89µs min=140.31µs med=191.7µs  max=17.36ms  p(90)=218.11µs p(95)=228.55µs
     ✓ { server:uWebSockets,mode:json-schema }...: avg=192.59µs min=142.11µs med=184.9µs  max=11.59ms  p(90)=206.96µs p(95)=214.17µs
     ✓ { server:uWebSockets,mode:no-schema }.....: avg=185.53µs min=136.62µs med=177.6µs  max=11.91ms  p(90)=199.41µs p(95)=206.88µs
     http_req_failed.............................: 0.00%   ✓ 0           ✗ 427783
     http_req_receiving..........................: avg=24.91µs  min=13.24µs  med=23.77µs  max=12.37ms  p(90)=29.02µs  p(95)=31.62µs 
     http_req_sending............................: avg=9.2µs    min=5.43µs   med=9.24µs   max=1.46ms   p(90)=12.27µs  p(95)=13.53µs 
     http_req_tls_handshaking....................: avg=0s       min=0s       med=0s       max=0s       p(90)=0s       p(95)=0s      
     http_req_waiting............................: avg=163.6µs  min=107.83µs med=155.2µs  max=17.28ms  p(90)=178.55µs p(95)=186.52µs
     http_reqs...................................: 427783  3564.818976/s
     iteration_duration..........................: avg=275.51µs min=196.12µs med=265.13µs max=17.52ms  p(90)=295.29µs p(95)=306.58µs
     iterations..................................: 427783  3564.818976/s
     vus.........................................: 1       min=1         max=1   
     vus_max.....................................: 2       min=2         max=2