feat: add void & never support

[nickthegroot]

Currently, void and never are failing with the following error:

UnknownZodTypeError {
  message: 'Unknown zod object type, please specify `type` and other OpenAPI props using `schema.openapi`.',
  data: {
    currentSchema: { type: 'never', error: [Function: error] },
    schemaName: undefined
  }
}

This was brought up in #290, although the closure felt a little premature: #290 (comment).

There isn't really anything that we can translate this to in terms of "open api specification"

I'm completely in support of this idea, although would advocate for the library gracefully handling these instead of erroring out. This is what this PR attempts to do. After all, if OpenAPI is meant to express what should be in the request, what shouldn't be in there has no relevance!

AI Disclosure: I used copilot to generate an initial plan and framework, particularly for the tests. All code was subsequently personally reviewed and edited.