schema.Type should be string or []string

[chancez]

Types are not only singular, but can be an array of valid types: https://json-schema.org/understanding-json-schema/reference/type

The schema.Type field currently only supports a single type currently, but should also support an array of types if many are provided.

I'd be open to implementing this myself, but wanted feedback before opening a PR.

1. Since this would be a breaking change, should I do it as a new field/struct tag?
2. How should it be implemented? I could add a new type:

type SchemaType struct {
  Type string
  Types []string
}

Or the existing value could be changed from string to []string, and in the singular case, it would just be a list with a single element. When rendering to JSON it could render it conditionally to a single string or a list, based on how many entries there are.

[samlown]

This is a really tricky one to implement in a strictly typed language like Go. A possible solution as you suggest would be to create a new type like type Type []string and provide a set of methods around it for serialization to and from a single string or array, depending on the number of entries...

[advdv]

This would usefull to us as well. Specifically because the OpenAI schema subset offers it as the (only?) way to make a property optional: https://platform.openai.com/docs/guides/structured-outputs#all-fields-must-be-required

@samlown Maybe this use off "null" in a sum-type scenario is common enough that it can be a flag on the Reflector that works with the "nullable" field tag. When both are enabled it would serialize the type: "string" as type: ["string", "null"]