`stream` should only accept type Boolean when using OpenAI API Server spec

[xvnyv]

The current behaviour of vLLM does not match the behaviour of OpenAI and Azure OpenAI when it comes to the stream parameter in the request body.

Current behaviour of OpenAI and Azure OpenAI:

• Only "stream": true or "stream": false are accepted. Setting "stream": "true" or "stream": "false" (or any other non-Boolean values) will raise the following error:

{
  "error": {
    "message": "'false' is not of type 'boolean' - 'stream'",
    "type": "invalid_request_error",
    "param": null,
    "code": null
  }
}

Current behaviour of vLLM:

• The following values for the stream request body parameter are accepted by vLLM: true, "true", false, "false"
• Any other values will raise the following error:

{
    "object": "error",
    "message": "[{'loc': ('body', 'stream'), 'msg': 'value could not be parsed to a boolean', 'type': 'type_error.bool'}]",
    "type": "invalid_request_error",
    "param": null,
    "code": null
}

• It seems like this is caused by the use of Pydantic with stream variable set to type bool instead of StrictBool (source code)

May I know if there is an agreement that vLLM should also reject the request when stream is set to the string values of "true" and "false"? I can prepare a PR to make the change if that is the desired behaviour.

[hmellor]

This was fixed in #116