Fix Choices Deserialization

Some OpenAPI Compatible APIs like Ollama don't always return `lobprobs`
as part of the `choices` JSON. To handle this we need to add a default
argument to `logprobs` so upickle can handle this case. A private case
class is used to avoid having to change the order of arguments which
would be a breaking change.

core/src/main/scala/sttp/openai/requests/completions/CompletionsResponseData.scala

@@ -2,6 +2,7 @@ package sttp.openai.requests.completions
 
 import sttp.openai.json.SnakePickle
 import sttp.openai.requests.completions.CompletionsRequestBody.CompletionModel
+import sttp.openai.requests.completions.CompletionsResponseData.Choices
 
 object CompletionsResponseData {
   case class Choices(
@@ -11,7 +12,14 @@ object CompletionsResponseData {
       finishReason: String
   )
   object Choices {
-    implicit val choicesR: SnakePickle.Reader[Choices] = SnakePickle.macroR[Choices]
+    // Unfortunately, some OpenAPI compatible APIs like Ollama don't always return `logprobs`, so we need to
+    // give it a default argument of `None`. Unfortunately, changing the argument order so we can do this
+    // would introduce a breaking change, so we need an intermediate private case class to handle this.
+    private case class ChoicesJson(text: String, index: Int, finishReason: String, logprobs: Option[String] = None)
+    private val choicesJsonR: SnakePickle.Reader[ChoicesJson] = SnakePickle.macroR
+
+    implicit val choicesR: SnakePickle.Reader[Choices] =
+      choicesJsonR.map(c => Choices(text = c.text, index = c.index, logprobs = c.logprobs, finishReason = c.finishReason))
   }
 
   case class CompletionsResponse(