feat: allow resolvers to set a custom response status code

[danielgtaylor]

Enable resolvers to return an error which satisfies huma.StatusError in order to set a custom response status code. This means the utility HTTP errors can be used, like huma.Error403Forbidden, if desired, but also anything that implements that interface will work.

Here's a minimal example:

type MyInput struct{}

func (i *MyInput) Resolve(ctx huma.Context) []error {
	return []error{huma.Error403Forbidden("nope")}
}

Note: errors are processed in-order and the last one wins. It's best to use this feature very sparingly.

Fixes #107.