Fix typespec generation for response oneOf

lib/ex_openai.ex

@@ -257,8 +257,17 @@ end)
  merged_required_args
  |> Enum.map(fn item -> quote do: unquote(ExOpenAI.Codegen.type_to_spec(item.type)) end)
 
- # convert optional args into keyword list
- response_spec = ExOpenAI.Codegen.type_to_spec(response_type)
+ # construct response spec
+ # for list types, instead of {:ok, list1 | list2}, we want {:ok, list1} | {:ok, list2}
+ response_spec =
+ case response_type do
+ {:oneOf, c} ->
+ Enum.map(c, fn comp -> {:ok, ExOpenAI.Codegen.type_to_spec(comp)} end)
+ |> Enum.reduce(&{:|, [], [&1, &2]})
+
+ etc ->
+ {:ok, ExOpenAI.Codegen.type_to_spec(etc)}
+ end
 
  optional_args =
  merged_optional_args
@@ -308,11 +317,11 @@ end)
 
  # fx without opts
  @spec unquote(name)(unquote_splicing(spec)) ::
- {:ok, unquote(response_spec)} | {:error, any()}
+ unquote(response_spec) | {:error, any()}
 
  # fx with opts
  @spec unquote(name)(unquote_splicing(spec), unquote(optional_args)) ::
- {:ok, unquote(response_spec)} | {:error, any()}
+ unquote(response_spec) | {:error, any()}
 
  def unquote(name)(unquote_splicing(arg_names), opts \\ []) do
  # store binding so we can't access args of the function later